The decision comes at the end of a week when the tournament was left in limbo after an attack on the Boca Juniors team bus as it approached the stadium for the second leg against arch rivals River Plate.

It is sad that such a shadow has been cast over the competition. The contest itself was beautifully poised at 2-2. It was the first time that the two Buenos Aires giants had met in the final of South America’s premier club competition since it began almost 60 years ago.

It was not the first time that this season’s competition had been blighted by fan violence. During a match between Pele’s old club Santos and Independiente of Argentina in São Paulo, fans threw missiles into the visiting dugout. It was eventually abandoned after 80 minutes and Independiente were awarded the overall victory.

Today, the authorities often step in to react to events outside the field of play but in 1971 a European Cup tie caused a sensation that made them re-write the rule book.

West German champions Borussia Moenchengladbach had produced one of the most spectacular performances ever seen to beat Internazionale of Milan 7-1 in the first leg of their second round tie.

Yet this remarkable match cannot be found in any of the record books.The result was expunged after a drunken spectator threw a Coca-Cola can which struck Inter striker Roberto Boninsegna.

UEFA ordered a replay and Inter went through on aggregate by virtue of a win in the San Siro.

Coached by the highly respected Hennes Weisweiler, Gladbach had won back-to-back Bundesliga titles. Their golden generation included stars who would form the spine of West Germany’s triumphant European Championship and World Cup side in the early 1970s. They included Berti Vogts in defence, midfielder Herbert Wimmer and striker Jupp Heynckes who were destined to enjoy a long and distinguished career both as a player and a coach.

But there was no doubting the star. Gunter Netzer, a mercurial and inspirational playmaker both for Gladbach and the national team.

A sell out 27,000 crammed inside the Bokelbergstadion that night and Heynckes scored the first goal early. Inter levelled soon afterwards through Boninsegna but less than two minutes later, the German side were back in front.

The incident which still provokes controversy today came in the 29th minute with the score at 2-1. A can was thrown from the crowd and hit Boninsegna who fell to the ground. As players surrounded the referee, Dutchman Jef Dorpmans, play was halted for seven minutes whilst Boninsegna received treatment for his injury.

Inter’s veteran Sandro Mazzola handed what appeared to be the offending can to the referee. Much later he revealed that the full can of Coca-Cola he had given to the match official was not the same one that struck Boninsegna.

Italian newspapers even published photographs of the receptacle which they said was 12 centimetres high and included diagrams of the incident. The can was thrown from a distance of six metres. The man said to have launched the can was 29-year-old Manfried Kristein, who was arrested and escorted from the ground. The match was continued on the instructions of the local police to prevent crowd violence.

Inter, meanwhile, claimed that the incident with the can had destroyed their composure.

Gladbach, for their part, cut loose before the half-time interval. Heynckes scored his second of the match in stoppage time to make it 5-1 at the break. They added two more in the second-half. Netzer scored with a deft first time chip typical of the man. Inter finished the match with 10 men after Mario Corso was sent-off for aiming a kick at the referee

It finished 7-1 and the score reverberated around Europe.

"That day we played the game of our lives," Netzer said much later. "No-one would have stopped us."

The reaction from the Italian club was rather different. "They were shocked and scared," claimed Inter head coach Giovanni Ivernizzi. Mazzola, an experienced campaigner who had played for Italy in the 1970 World Cup insisted that "the match was over at 2-1".

After the match, Inter's vice-president Peppino Prisco sought out Sir Matt Busby, the former Manchester United manager, who was UEFA match observer, and informed him that his team wished to make a protest.

As part of their evidence, they submitted the referee’s written report.

When UEFA met they considered the punishment to be given to the German club. There was a fine of CHF10,000 and they were forbidden to play their next home match at their own stadium. The venue for the replayed first leg with Inter would be the Swiss city of Bern.

It was, said Gladbach coach Weisweiler, "a very hard blow. This has practically defrauded us of victory".

Now it was the Gladbach's turn to protest. Another UEFA hearing was planned to hear the appeal but, in the meantime, the second leg of the tie was played at the San Siro Stadium in Milan.

Some 1,300 police were called up for the night and mindful of the drinks container which had caused all the trouble, refreshments at the ground were served only in paper beakers.

Inter scored twice in the first 13 minutes and remained in control of the match throughout. They eventually won 4-2.

The appeal was heard and UEFA bosses modified the punishment. What had originally been the first leg should now be played at least 100 kilometres from Moenchengladbach. The venue chosen was the Olympic Stadium in Berlin.

Dr Artemio Franchi, President of the Italian Football Association who would later become UEFA President, described the stance as "a courageous and sporting decision which will calm down all those who have at heart the success and good conduct of international activity".

Where the original match had produced eight goals, this ended goalless and was described by one neutral observer as "brutal". Inter went through.

The match that never was still stirs the passion. Uwe Seeler, a veteran of five World Cups with Germany, made his opinion clear and even accused Boninsegna of play acting. "Borussia won by seven goals to one," he said. "This clear defeat cannot be explained by the absence of Boninsegna."

Much later, referee Dorpmans told the German magazine Spiegel: "I am convinced that Boninsegna played being unconscious, a mature acting performance."

Many were concerned that UEFA's decision opened the way for copy cat agent provocateurs to force the abandonment of a match in order to influence the result.

Incidentally the referee later donated the can to the Vitesse Arnhem museum where it was displayed for almost 40 years before being sent back to Moenchengladbach. It is now part of their museum.

Inter went on to reach the final of the competition that year where they lost to Ajax.

"It is a decision which fits perfectly, a verdict which can satisfy everyone. It was not excessive punishment on Borussia who after all were not responsible for throwing the bottle(sic) which knocked out Boninsegna," said Mazzola.

By a strange coincidence Inter had been involved in a similar incident during a World Club Championship final against Independiente in Buenos Aires during the 1960s. Their Spanish midfielder Joaquin Peiro was hit in the face by a missile, thought to be a bottle. Instead of falling down, he carried on playing. Inter went on to lift the World Club Cup.

The Boninsegna incident came at the start of a dark decade when fan violence would cast a malevolent shadow over European competition. 

It reached its nadir in the mid-1980s when English clubs were banned from European competition for five years after numerous incidents which caused many on the continent to call football hooliganism "the English disease". The last straw had been the violence at the 1985 European Cup final at the Heysel Stadium in Brussels. Liverpool supporters launched an attack on fans of their opponents Juventus which left 39 dead. On this occasion the game also went ahead on the recommendation of the police.

In Germany this week, the courts jailed a defendant identified as Sergei W. for 14 years after finding him guilty of 28 counts of attempted murder after he detonated three explosive devices near the Borussia Dortmund team bus before a UEFA Champions League match in 2017.

The world waits to see what punishment CONMEBOL will mete out after the frightening episode in Buenos Aires but staging the second-leg of the final in Madrid will have a symmetry of sorts. 

When the Copa Libertadores was conceived, it was to give South America a way of finding a champion club to challenge the European club champions in an "Intercontinental Final", the forerunner of the present FIFA World Club Championship. The dominant team in European club football at that time were, of course, Real Madrid.