It is easy to forget where the Champions League came from.
Three decades ago European football's governing body Uefa sometimes didn't know what day games would be played until 48 hours before kick-off. In the first Champions League season, some of the players were still part-time.
The 1992-93 inaugural edition started with two knockout rounds between September and November. Leeds and Stuttgart ended up playing a neutral venue decider for their first-round tie, in front of 90,000 empty seats at Barcelona's Nou Camp - after the German side broke Uefa's rule on only fielding three foreigners.
Eight teams progressed to make two groups of four, with games played from November to April. The group winners met in the final. Marseille - who would have their 1993 French league title stripped over match-fixing - beat AC Milan 1-0 on 26 May.
Rangers went undefeated but finished just a point behind Marseille. Second to Milan were IFK Gothenburg.
"Before a home group game against Porto, me and a friend were at work at 7am and then played at 8.45pm," recalls ex-Gothenburg and Sweden midfielder Hakan Mild.
"We were semi-professionals. We trained a lot, not less than Porto. But we didn't have the same financial situation.
"Portuguese media were there and made a film for television. The TV people said it was unbelievable we were working and it was not possible to beat Porto, who had a good team in that period."
Gothenburg won that match 1-0.
There was one club per country. The champions of Scotland and Sweden were essentially semi-finalists. It sounds like a quaint, bygone age - far removed from the global phenomenon we recognise now. But it still represented a big break from what had gone before.
The European Cup had been going since 1955 but the bigger clubs weren't happy with it. The 1980s saw periodic agitation for a new - and more commercially rewarding - competition. AC Milan owner and media giant Silvio Berlusconi was one of the ringleaders.
The argument - which remains to this day and is at the crux of the controversial European Super League debate - was that because the best supported clubs drive revenues by attracting the most viewers on TV, they should get more money.
Uefa, just as it is now, was forced to navigate the tightrope of giving those clubs what they want while trying to maintain an inclusive competition.
"The clubs were always coming up with proposals that could have more matches and guarantee more money," says Gerhard Aigner, who served as Uefa's general secretary from 1989 to 2003.
"We still had a knockout system and in the European Cup we had only one team from each country, so only five teams from the five big TV markets. The same in the Cup Winners' Cup.
"But in the Uefa Cup, countries had more than one team. There were more matches and more chances of clubs from the bigger markets meeting. Commercially that became a competition that had more potential than the European Cup.
"It became impossible. We realised that if Uefa didn't act and take things in our own hands, we would probably lose control of these competitions altogether."
Its new competition, the Champions League - with its theme tune, its new broadcast package, its expanded format - was an immediate success.
"We wanted to make it as attractive as possible for the supporters, for TV and for the clubs themselves," says Aigner.
"We managed to have two experts joining us who had just left ISL [Swiss marketing company International Sport and Leisure]. They had marvellous ideas and they developed great ideas about how to present a new product to the public. We also looked across the ocean at the American way of organising the Super Bowl.
"We not only could impress in terms of finances, we could also impress in terms of presentation of the competition, and probably also behaviour of the teams on the pitch.
"The players realised they were playing on a different level. They were more conscious of the fact they were now on this platform where they have to give a certain example. I don't know whether that's still the case today, but during a certain time I had the feeling we have a better product on the field than before.
"I think even the clubs themselves and the respective national leagues were surprised how that was being done."
Aigner felt that Uefa had pulled it off, appeasing the big clubs while maintaining sporting integrity and competitive appeal. In 1992-93, defending champions Barcelona didn't make the group stage - CSKA Moscow knocked them out.
But things would evolve very dramatically, and very quickly.
Over the first two seasons of the new Champions League, the English clubs involved - Leeds and Manchester United - failed to make the group stage. In the inaugural campaign of 1992-93, Spanish and German sides were absent too.
Uefa decided that to maximise income, broadcasters from the richest European countries needed to be encouraged to lodge higher bids. So changes came in for 1994-95.
The champions of eight countries - including England, Italy, Germany and Spain - went straight into a group phase expanded to make four groups of four.
As the qualifying process was stripped back, 22 national league winners - including those of Bulgaria and Norway - were excluded altogether and shoved into Uefa Cup qualifying instead.
Then, in 1995, the Bosman ruling changed employment regulations for football players. As a result, Uefa's rule that clubs could only field a maximum of three foreign players (plus two who had played in that country for an uninterrupted period of five years, including three as a junior) had to be scrapped.
Former Rangers midfielder Stuart McCall credits the '3+2' ruling with making his career. He was signed by the Scottish club in 1991, the same year as '3+2' was introduced.
"People talk about Sliding Doors moments," says Leeds-born McCall, now 58.
"In 1984 I was on the bench for England Under-21s in Turkey. I was on the touchline to come on and that would have made me English in terms of the representative game.
"But the referee blew his whistle and I never got on. That allowed me to change my mind and become Scottish. If I had got on, I probably would not have made my way to Rangers."
For Aigner, the Bosman ruling had a major influence on how European football has been transformed since. But he also looks back on "mistakes made" by Uefa.
He says: "We couldn't know about the decision that would be taken in the European Court over the Bosman case. That unbalanced the whole situation because those clubs who, until then, were able to compete with their own talents on the highest level couldn't do it any more as they started to lose their talents at a very early age.
"Also, we didn't get the financial distribution model right in the national context because the money coming to the clubs from Europe only went to those playing European football.
"But the other mistake we made was to help the big clubs by giving four places instead of two. As long as we had two and two had to qualify, the other countries with their champions had a real chance. Now the door is too small for them to enter the competition."
In 1997, Lennart Johansson was Uefa president and Aigner its general secretary when runners-up from the eight highest-ranked leagues, according to Uefa coefficients, were allowed into the Champions League for the first time. All eight entered at the final qualifying round and all made it to the group stage. Seven out of the eight quarter-finalists that season were from one of the 'big five' leagues - England, Germany, Italy, Spain and France.
It was the start of a pattern. Every season since has seen at least six of the last eight made up by teams from those five leagues. On four occasions they've contributed the entire quarter-final line-up.
In 1999-2000 there were further changes, with four teams from the biggest three leagues allowed in, two through the qualifiers. In 2009-10, three clubs from England, Italy and Spain went straight into the group phase. In 2018-19 four teams from the biggest four leagues went straight into the group phase and the number of qualification spots went down from 10 to six.
Now 16 clubs from England, Spain, Italy and Germany account for half of the group stage. These changes have meant more games involving the richest clubs and most high-profile players.
And the biggest move is set to come.
In 2024 the Champions League will scrap the group stage as it expands again, becoming a single league of 36 teams in which each side plays 10 games against 10 different clubs, half at home and half away.
Two of the additional four spots will be allocated to teams who performed best in Uefa competition the previous season. This season, Arsenal and PSV Eindhoven would have been invited in.
It is a controversial move, watered down from initial proposals that would have rewarded teams based on their previous five years' European performances, almost always favouring the biggest and most successful countries.
Plenty don't like what remains.
"It is not the same. It is an industry today," says 51-year-old Mild, who had four spells with Gothenburg between 1989 and 2005.
"It was not an industry 30 years ago. It's maybe because I am getting older but it was more real in that period. It was not fake. There was more heart in it."
The forthcoming expansion was negotiated partly by Juventus chairman Andrea Agnelli in his role as European Clubs' Association (ECA) chairman. However, before it was launched Agnelli quit from the ECA, along with representatives from all 12 clubs involved in the shambolic European Super League (ESL) launch of 2021.
That idea has not gone away. A European Court of Justice ruling is due in the spring on whether Uefa should have a monopoly on organising pan-country international tournaments. If it comes down in favour of Juventus, Barcelona and Real Madrid - the only clubs yet to formally withdraw from ESL plans - the Champions League is unlikely to be around to celebrate a 40th birthday.
"It's unfortunate," says Aigner, now 79.
"The sport's authorities can't really exert [the] control that would be desirable for sporting reasons because of competition rules.
"In my time, I sent someone out to Australia to study what [Rupert] Murdoch had done to football [rugby league] out there. It almost destroyed the game by creating a rebel league.
"But we see every day that money speaks louder. We have the World Cup in Qatar. We have the example of the [LIV] golf competition. Golfers are split in their feelings about that.
"I do understand the principle of open markets and freedom and so on. But if you look at the Premier League, most of the clubs belong to people from elsewhere. Is that what we want? Is that what the government wants?
"What can be the interest of the owners of the clubs in the UK in European football? Can they have an interest in European football? I doubt it.
"I am afraid I am someone of an age who still has the old values, which I would like to remain."