When Barcelona celebrated the league and Champions League double by ­beating Arsenal in Paris in 2006, a familiar face was missing from the photograph. Lionel Messi, returning from a muscle injury, thought he was ready; the coach, Frank Rijkaard, did not. The Argentinian, silently simmering, did not join in the celebrations. Now, he has the chance to make amends: on Wednesday night in Rome Messi will play what he last night described as "the most important game of my life".

Victory in Paris three years ago meant it was not a decision that haunts Rijkaard but it is a decision that still haunts Messi. It is also a decision that is utterly unthinkable now. With Pep Guardiola carefully rotating throughout the year, Messi has remained fit all season for the first time in his career and will be rested for tomorrow night's clash with Osasuna to guarantee his presence. Asked how he and his team-mates were, he simply grinned and replied: "Spectacular."

"We have had a fantastic season already," Messi said. "Now we can achieve something historic." He is not wrong: no Spanish side has ever won the league, Copa del Rey and Champions League in a single season. Barcelona are two-thirds of the way there. There is another title up for grabs, too, however hard Messi tries to hide from it – for many, the world's finest footballer will be decided by this match.

So, too, may the planet's finest team. Rome will not, Messi said, be a monologue with one team parking the bus, as it was against Chelsea. It will instead be "good for the game" and give Barcelona a chance to show their true class.

"There's no doubt that these are the best two teams in the world right now," Messi said. "And I wasn't able to play in Paris so this will be the most important game of my life.

"We deserve to win the Champions League because of the football we have been playing all year – people admire what we have done.

"Everyone knows Cristiano Ronaldo so well that I don't think they need me to tell them how good he is. He's a great player. He's a player who is very hard to stop; he scores a lot of goals and he can change a game in an instant. He is a player who has everything. But Cristiano and I are only focused on our teams; what matters to both of us is which team wins, not which player."

Messi was open in his criticism of Chelsea after the semi-final, claiming that justice had been done with ­Barcelona going through and he believes that Manchester United will be a different proposition. Even last year's semi-final, when Sir Alex Ferguson's side won 1-0 on aggregate after two games that they approached with a decidedly defensive mind-set, did not prevent him from likening the Premier League champions to the Barcelona side who have scored more than 100 league goals this season. Messi believes that United will open up – and that will suit the Catalans.

"Manchester United are not going to play the same way that Chelsea did. They're going to try to play football and I think it's going to be a much more open game than the match against Chelsea was. That's good for football and it's good for the fans," he said. "They play a very similar type of football to us; they move the ball around on the ground, they are an attacking team who play three up front and have excellent strikers, like Ronaldo and [Carlos] Tevez."

There was, though, a hint here that Messi does not know a huge amount about his opponents. Asked about Patrice Evra, his likely marker on Wednesday night, there was a pause, a laugh and the sneaking feeling that the Argentinian had never heard of him. "He is," Messi said simply, "a great player."

If Messi knows little, Guardiola is a very different proposition. And nor is he so sure that United will attack. He admitted that last season's semi-finals were the first two games that he watched on video but he said he has more viewing to do yet."I have seen some interesting things and they are a very dangerous team," Guardiola said. "Above all we are going to have to play with intelligence and try to dominate possession. What Ferguson has done is incredible; he has won so much. It's an honour to be able to play a final within a year of becoming a coach and be able to play against Alex Ferguson. It makes me proud to face him."