Antonio Rudiger in danger of missing Real Madrid's Champions League clash with Man City | OneFootball

Real Madrid centre-back Antonio Rudiger faces a race against time to be fit for the upcoming Champions League double-header against Manchester City.

The totemic defensive presence limped off just 15 minutes into Madrid's shock 1-0 defeat to Espanyol on Saturday night. While Carlo Ancelotti raged against the refereeing, he also fretted over the potential absence of his star centre-back.

"He's had a muscle injury, they'll have to assess it," Madrid's manager revealed post-game. "We know what we have to do, we've thought about it and we've talked about it."

The club officially confirmed Rudiger's prognosis on Sunday. "Following tests carried out on Antonio Rudiger by Real Madrid's medical services, the player has been diagnosed with an injury to the biceps femoris in his right leg," a statement read.

Antonio Rudiger has not missed a single La Liga game this season / Alex Caparros/GettyImages

While Madrid didn't provide a timeline, the Spanish publication MARCA estimated that Rudiger would be ruled out for around 20 days.

The German has been an ever-present for Madrid in a season when Eder Militao, David Alaba and Dani Carvajal have all been sidelined for long spells. If Rudiger is forced to sit out the next three weeks, he could miss a glut of crucial fixtures.

Real travel to Leganes in the Copa del Rey quarter-final in midweek before hosting Atletico Madrid next Saturday in an almighty capital derby. Beyond the bragging rights, both sides are locked in a competitive title race with Barcelona at La Liga's summit.

Then there is the minor significance of a two-legged tie against Manchester City. The European behemoths were paired together in the Champions League knockout play-offs and face off at the Etihad Stadium on Tuesday, 11 February - halfway through Rudiger's reported recovery period.

Madrid host City in the second leg of that blockbuster European tie on 19 February, which is just before the 31-year-old's theoretical return.

David Alaba is fit again but Ancelotti will be wary of overworking the Austria international after he sat out more than a year with an ACL tear. Academy graduate Raul Asencio is a natural - if inexperienced replacement - while defensive midfielder Aurelien Tchouameni has regularly been forced to moonlight in defence, with mixed success.