LONDON - Manchester United manager David Moyes says that his side must exploit the smallest weaknesses in Bayern Munich's game if they are to eliminate the Champions League holders in the quarter-finals. United appeared in three of the four finals between 2008 and 2011, triumphing in the first year, but their fall from grace under Moyes means that they approach Tuesday's first leg at Old Trafford as underdogs.While Bayern have grown even stronger under their new coach, Pep Guardiola, sweeping to a successful Bundesliga title defence in record time, United have endured a torrid campaign. Seventeen points behind Premier League leaders Liverpool and 10 points below the top four, their season now hinges entirely on their last-eight encounter with the all-conquering Bavarians."When we drew them, I felt we'd drawn probably the best team in Europe at this present time. I think most people would agree with that," Moyes said. "We have got a really tough game and know exactly what we are going to get, but we'll try to exploit little bits of weaknesses they have got. Pep has taken over a really good team and added a bit himself with his own style. They have already won the Bundesliga quite comfortably, so the focus is on the Champions League now."Moyes's maiden campaign at United has been a succession of false dawns and crashing lows, and their recent form provides few assurances. Although they came back from two goals down to beat Olympiakos 3-0 in the last 16, this month has also seen the English champions humbled 3-0 at home by both Liverpool and Manchester City.Last season's top scorer Robin van Persie is currently sidelined after spraining his knee against Olympiakos, but the form of Wayne Rooney, at least, gives United reason for optimism. Rooney's brace in Saturday's 4-1 defeat of Aston Villa took his tally to four goals in three games, and his creativity will be especially important in the absence of the cup-tied Juan Mata.A group of United fans chartered a plane to fly over Old Trafford towing a 'MOYES OUT' banner during the Villa game, and although the Scot received a warm reception inside the ground, his position will again come under scrutiny if his side are embarrassed by Bayern. It will not be lost on United's fans that Guardiola was once seen as an ideal successor to their former manager Alex Ferguson, whose retirement last year paved the way for Moyes's appointment.Having turned Barcelona into the first truly great team of the 21st century, the Catalan now has his sights set on improving a Bayern side that claimed an unprecedented treble under Jupp Heynckes last season. Bayern are bidding to become the first side ever to complete a Bundesliga season unbeaten and to win back-to-back European Cups in the Champions League era. They have already impressed in England twice this season, outclassing City 3-1 in the Champions League group phase in October and then beating Arsenal 2-0 in the last 16.However, Guardiola was critical of his players after they threw away a 3-1 lead in a 3-3 draw at home to Hoffenheim on Saturday, which was the first time they had dropped points in the league since October 5. "We need to analyse what happened," he said. "If we play like we did today in the second half, we are not the favourites on Tuesday against Manchester."The draw came at the additional cost of a knee ligament injury to midfielder Thiago Alcantara that could keep him out for eight weeks, while centre-back Dante will also miss the game at Old Trafford through suspension. United, meanwhile, could have serious problems in defence. Left-back Patrice Evra is suspended and there are fitness concerns over Rio Ferdinand, Chris Smalling, Jonny Evans and Rafael. United famously beat Bayern 2-1 in the 1999 Champions League final, but the German giants have since prevailed twice when the teams have met in the last eight, most recently in 2010.