Gary Lineker says Manchester United will only win Saturday's Champions League final at Wembley if Barcelona play badly.
Barca beat United in the 2009 final and are tipped by many to repeat their Rome success this weekend.
"If Barcelona turn up, they win," said former England captain Lineker, who has also played for the Spanish giants.
"Barca have got to have a bad day for United to realistically have a chance. Either that or United get lucky."
Lineker did concede that, with the game being a one-off played in England, United had a chance of prevailing, but insisted that La Liga champions Barcelona were heavy favourites.
"The fact it is in England and they will probably get the vast majority of the support and it is 90 minutes, not two legs, gives them a better chance," said the BBC presenter.
"But if they played 10 times, United might win one or two of them, there would maybe be a couple of draws and Barca would win the rest."
Both sides head into Saturday's final as recently crowned champions of their respective domestic leagues.
However, whereas it has been suggested that this United side does not match up to some of the previous teams constructed by manager Sir Alex Ferguson, Barca's current crop of players are being hailed as potentially one of the best squads assembled in club football history.
Under current coach Josep Guardiola they have won three consecutive La Liga titles, the Copa del Rey in 2009 and the Champions League the same year, when they overcame United 2-0 in the final.
They are also lauded for their attractive, passing style of football.
And Lineker believes Guardiola's side has the capability to become the greatest ever seen in club football - adding his voice to Monday's discussion on Radio 5 live as to the greatest club side to have played.
"Time will tell, but potentially they could be the best club side ever," claimed Lineker, who played at the Nou Camp between 1986 and 1989. "They are on their way to possibly doing so.
"They are going to compete with the great club sides; the great Liverpool teams, the AC Milan side and Real Madrid of way back.
"But to do that I think they have got to be prolific winners of the Champions League.
"If they can beat Manchester United and then win two or three more in the next few years, with their style of football, in the modern game, they could well become the best side ever.
"They are certainly the best side I've witnessed in terms of the attractiveness of their football, the way they have moved the game on."
United, meanwhile, might not have been as easy on the eye as Barcelona this season but Sir Alex Ferguson's side still had enough to win the Premier League by nine points.
This takes Ferguson's Premier League trophy tally to a remarkable 12. He has also won the FA Cup five times, the League Cup on four occasions, the Cup Winners' Cup once and the Fifa Club World Cup once.
The 69-year-old Scot is aiming to make it a hat-trick of Champions League triumphs on Saturday.
"I think Sir Alex Ferguson is already the greatest British manager," said Lineker. "He is not just one of the greatest British managers but one of the greatest in world football.
"His record speaks for itself. It is there to compare with anyone and it is better than anyone.
"He has already won the Champions League twice, he has won 12 titles and numerous FA Cups and everything else that goes with that.
"Even if they lose this one it won't be down to him, it will be because Barcelona are a truly incredible side."
Lineker admitted that Ferguson has his work cut out if he is to mastermind a victory over Barcelona.
"It is going to be very difficult," he said. "The problem you have with Barcelona is getting the ball off them.
"I think Alex will play the way he has been playing in recent weeks with Hernandez up front, Rooney off him, flood the midfield as much as he can and counter-attack as quickly as possible.
"But Barcelona are so good, you can have all the plans in the world but if [Lionel] Messi, [Andres] Iniesta and Xavi are on song, you are in trouble. United's best chance is if Messi pulls up in the warm-up!"
Lineker left Everton to join Barcelona in 1986, signing for £2.75m.
He scored 44 goals in 99 games during his time in Spain, which gave him an insight into the importance of Barcelona the football club to the people of Catalonia.
"The identity of Catalonia is hugely important to the Barcelona fans," said Lineker.
"They have got a little saying, 'més que un club' which translates as 'more than a club' in Catalan.
"What they are saying by that is that it all goes back to the repression Catalonia and various other places in Spain suffered during the Franco reign, where they weren't allowed, for example, to speak their own language.
"The one place they could possibly do it and get together was in the Nou Camp. In many ways that became their focal point against Franco's Madrid.
"That is where that great rivalry with Real Madrid comes from - it is more than just a football match, it means much more politically and historically.
"Obviously time passes and memories fade, but it remains, there is an undercurrent there. That is why this great team they have now gives them more pleasure than it would otherwise do so."