Bayern sweating over Alaba's availability for Dortmund cup semi

Berlin - Carlo Ancelotti says Bayern Munich is holding its breath over David Alaba for Wednesday's German Cup semi-final against Borussia Dortmund after the Austria international injured his knee.

Alaba switched from left-back to central defence, but limped off after just 16 minutes of Bayern's 2-2 draw at home to Mainz on Saturday and Ancelotti is waiting to see the extent of the injury.

"He couldn't continue. He had a small problem in the knee, which we are now checking, but it's not a big problem," said Bayern's Italian coach Ancelotti.

"We'll see if he can play on Wednesday."

Bayern is already struggling in defence with Germany 'keeper Manuel Neuer sidelined for the rest of the season with a foot fracture.

Ancelotti was without injured centre-backs Javi Martinez and Jerome Boateng against Mainz, but the pair should be fit to face Dortmund in a repeat of last year's cup final which Bayern won on penalties.

Bayern needed a Thiago Alcantara equaliser to seal Saturday's 2-2 draw as it twice came from behind against relegation-threatened Mainz to maintain its 20-match unbeaten record at home in the Bundesliga.

Second-placed RB Leipzig can trim Bayern's lead in Germany's top flight to six points if it wins at Schalke on Sunday with the Bavarian giant chasing a fifth straight German League title this season.

Dortmund, who also bowed out of the Champions League in midweek after losing its last eight tie at Monaco, also has defensive woes as it looks to reach the German Cup final on May 27 at Berlin's Olympic Stadium.