Carlo Ancelotti says Bayern Munich are holding their 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 are already struggling in defence with Germany goalkeeper 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 they twice came from behind against relegation-threatened Mainz to maintain their 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 they win at Schalke on Sunday with the Bavarian giants chasing a fifth straight German League title this season.
The draw with Mainz capped a week to forget for the Bundesliga league leaders following Tuesday's Champions League quarter-final exit at the hands of Real Madrid.
Dortmund, who also bowed out of the Champions League in midweek after losing their last eight tie at Monaco, also have defensive woes as they look to reach the German Cup final on May 27 at Berlin's Olympic Stadium.
Their centre-back Sokratis Papastathopoulos is carrying a leg knock.
The Greece international sat out Saturday's Bundesliga match at Borussia Moenchengladbach, but Dortmund has "ruled out" him facing Bayern, according to their website.