Manchester United’s already ominous task of taking on European champions Bayern Munich in the first leg of their Champions League quarterfinal tie at Old Trafford on Tuesday could be exacerbated by having to field a makeshift defense.

Already without left-back Patrice Evra through suspension, right-back Rafael was forced to miss training on Monday with a thigh problem. United’s defensive options have already been depleted in recent weeks with injuries ruling out Chris Smalling and Jonny Evans. The pair were involved in training ahead of the game, although it is unlikely that Evans will be given a starting role given that he has not featured since the start of February.

Smalling, who has played at right-back on several occasions this season, would look to be favorite to take the right-back role should Rafael fail to recover in time. Antonio Valencia, who has also returned to training following a recent injury, could in theory deputize but will surely be judged too much of a defensive liability going up against Franck Ribery. The prospect of the massively defensively suspect Alex Buttner trying to defend Arjen Robben should already fuel enough concern at Old Trafford.

But Manchester United’s problems extend far beyond their defense. United are just a point away from having mathematically relinquished their Premier League title in March, while in contrast Bayern Munich have already retained their Bundesliga crown. As the Bavarians have ascended to become Europe’s preeminent club, reaching the final for the past two years and lifting the trophy last season, United have fallen considerably since reaching three finals in four years.

The genesis of United’s decline has been apparent since the Champions League final of 2009. Not only was the defeat the last match before Cristiano Ronaldo exited for Madrid with his superstar quality yet to be replaced, but it was also when it became obvious that United’s midfield was unable to match Europe’s best.

Almost five years on and that remains the case. In the intervening time only one central midfielder has been signed, yet the £27.5 million capture of Marouane Fellaini has not addressed United’s chief needs. Michael Carrick has been a fine passer but has too often been a nonfactor when United tackle the best opposition. While he has struggled to affect a game when put under pressure, it is also true that he has not been helped by the failure to supply him with a partner who can complement his lack of mobility. In both the 2009 and 2011 final, Ryan Giggs lined up with Carrick in a midfield that was completely bypassed by Barcelona’s passing master class. Now having entered his fifth decade, the feeling is that Giggs will start at Old Trafford on Tuesday.

And there is every reason that the man who masterminded those final defeats for United, Pep Guardiola, will serve up another comprehensive win this time around. Bayern have now usurped his former club in having the best midfield of any club in the world. While they may not quite have as complete and brilliant a trio as Busquets, Xavi and Iniesta at their peak, Guradiola now has a startling array of options at his disposal.

Those choices have been reduced with Thiago Alcantara missing the opportunity to show United first-hand what they missed out on when failing to sign him last summer. The former Barcelona man’s knee injury, which will rule him out of both legs, is compounded by a suspension to Dante that is likely to mean Javi Martinez dropping into the back line. Still Bayern can choose between a rather handy selection of Philipp Lahm, Bastian Schweinsteiger, Thomas Muller and United target Toni Kroos. Each one would be an undoubted star at Old Trafford.

If there is a weakness in this Bayern side it is in the area where Martinez is likely to be deployed. While the Spanish international is a solid presence there, and Jerome Boateng and Dante are fine defenders, they are arguably not up to the class of the rest of their team and can on occasion look flustered. Arsenal certainly troubled Bayern in the early stages of their first leg tie when playing with a boldness and intensity that initially caught the Bavarians out having regularly been met with relatively meek opposition domestically.

However, it is hard to imagine Moyes, the arch pragmatist, playing with such adventure. United’s best performances this season have come with either Shinji Kagawa linking up with Rooney from the No. 10 spot. Yet, Moyes has continually failed to trust either in that role against the better teams. With Mata suspended, Kagawa, too, looks an unlikely starter.

Further troubling for Manchester United is that there is no suggestion that they are capable of a heroic backs-against-the-wall performance that with a bit of luck could see them overcome more talented opposition. That approach worked for Chelsea on their route to the trophy in 2012, but United simply don’t have either the history or mentality for that strategy, even with a full-strength defense. And Moyes, who if anything proved that he could set up a side to be defensively solid when at Everton seems to have lost his ability to even do that successfully. The loss to Manchester City was a case in point. The Scot’s unfathomable formation that had Tom Cleverley and Marouane Fellaini lined up either side of Michael Carrick seemed to confuse even the players as they wandered all over the pitch in a shambolic mess.

While rumors of dressing-room unrest continue to be denied, the evidence is overwhelming on the pitch that a large number of the players are not relishing working under Moyes’s stewardship. Too circumspect to pressure Bayern and not resolute or well-organized enough without the ball, Bayern’s class will tell in an encounter that could be even more definitive than those two finals against Guardiola’s former charges.

Prediction: Manchester United 1-3 Bayern Munich