Rio Ferdinand believes the nagging fear of failure will drive Manchester United towards glory.

United now know they will face Barcelona in Rome's Olympic Stadium on May 27 when they attempt to become the first side to successfully defend the Champions League.

It is the second half of a double achieved last season that, if repeated, would allow the current crop of Red Devils to join the list of immortals.

But with seven points still required from four games to clinch a hat-trick of Premier League titles, Ferdinand is taking nothing for granted.

"I'll only be able to tell you after the final whether we are the best United team or not," said the 30-year-old.

"We haven't won anything this season.

"If we don't win the league and Champions League went belly up then we wouldn't be talked about as a successful side, let alone the best one, so we still have a lot to play for."

In all probability, if United come through Sunday's Manchester derby at Old Trafford, an 18th league championship will be theirs, allowing Sir Alex Ferguson's men to draw level with the record of Liverpool that has lasted since 1990.

After their mini-blip just before the last international break, when defeats to Liverpool and Fulham appeared to plunge United to the brink of crisis, it seems they have hit top form again.

Ferdinand would not swap the men in his dressing room for those at Anfield or the Nou Camp.

And, in Cristiano Ronaldo, they have a player eager to retain his status as number one in the world ahead of Lionel Messi.

Ronaldo stunned the Emirates Stadium with a 40-yard free-kick on Tuesday and followed up with his 25th goal of another incredible season - a figure even more remarkable because he started a month behind everyone else after a summer ankle operation.

"People forget Cristiano had an operation at the start of the season," said Ferdinand.

"It takes time to get over that. He has done well to recover so quickly and now I think we are seeing the Cristiano Ronaldo everyone knows."

Ferguson will have to raise the spirits of Darren Fletcher, who knows he must watch from the stands in Rome, just as Paul Scholes and Roy Keane did at the Nou Camp 10 years ago.

However, such is the strength of Fletcher's character, he could well be involved against City, with Ferdinand giving away its importance as a title decider.

"I don't want to build it up too much because we could win the derby on Sunday but still lose the next three games," he said.

"But we need to beat City.

"It will be a tough game. They have won their last couple of matches and are on a bit of a roll, so they will feel they can come and do a job on us. It is up to us to make sure it doesn't happen.

"I am not really sure whether they have something to prove but we still do."