Manchester United's Wayne Rooney faces a race against time to be fit for Wednesday's Champions League quarterfinal, second leg at Bayern Munich with the host winless in its past three matches.

European champion Bayern suffered its first Bundesliga defeat in 18 months when it was beaten 1-0 at Augsburg on Saturday following last Tuesday's 1-1 first-leg draw with United at Old Trafford.

Centerback Nemanja Vidic's header put United ahead in the first leg at Old Trafford only for Bayern's Bastian Schweinsteiger to equalize before being sent off for a second yellow card on the stroke of 90 minutes.

Bayern coach Pep Guardiola has described Wednesday's second leg at Allianz Arena as a matter of "life or death" for holder Munich, which has made no secret of its desire to become the first team to defend the Champions League title.

United's hopes hinge on Rooney, who missed Saturday's 4-0 league win at Newcastle United with a badly bruised toe, and the 28-year-old's absence would be a big blow to United's chances of advancing.

Along with Robin van Persie, who is out with a knee injury, Rooney is the club's top scorer this season with 17 goals, two of which were in the Champions League.

"If he is out, it would certainly be a big loss for United," said Bayern centerback Jerome Boateng, whose job would be to contain the England star.

"Wayne Rooney is the key man for United; he always makes himself available and he goes looking for the ball. He is always good for a goal."

United trails Premier League leader Liverpool by 17 points, but manager David Moyes has the chance to redeem himself after a wretched first season in charge by claiming Bayern's scalp.

"We always believe when you play for Manchester United. It is not because we won 4-0 against Newcastle that we start to believe we can win against Bayern," said United star Patrice Evra, who missed the first leg through suspension.

The Red Devils will be without cup-tied Juan Mata, who scored twice and created a goal at Newcastle, and Bayern's Boateng fully expects United to come to Munich and defend.

"Just like in the first leg, they will try and get at us on the counter attack and at set plays," said Boateng.

"We need just a little more pace, we need to get our crosses in a little quicker, and we should sometimes try our luck with shots from long range."

United travels to Bavaria with the host needing a return to winning form since hitting a rough patch after securing the Bundesliga title two weeks ago with a record seven games to spare.

Guardiola will have to make a few more changes for the second leg, especially in midfield with Javi Martinez and Schweinsteiger suspended.

Attacking midfielders Thiago Alcantara and Xherdan Shaqiri are injured, but Guardiola still has plenty of options, including Philipp Lahm, Arjen Robben, Toni Kroos, Mario Goetze and Franck Ribery.

Bayern only needs a scoreless draw to go through, but the holder wants a convincing win after recent results.

"We have got to play to win. We will end up losing if we play for a goalless draw," said Bayern's Brazil centerback Dante, who will return having been suspended for the first leg.

"We've got to be aggressive going forward from the start and try to score.

"Manchester United will sit back again. They will take more risks the longer the game goes on."