Real Madrid have confirmed that defender Raphael Varane has suffered a hamstring injury.
The France international was substituted in the second half of Wednesday's 2-1 LaLiga defeat to Valencia, with head coach Zinedine Zidane confirming that the player had complained of discomfort in his left leg.
"Following tests carried out today [Friday] on Raphael Varane at the Sanitas La Moraleja University Hospital, he has been diagnosed with a grade two muscle strain in his left hamstring. His recovery will continue to be assessed," Madrid said in a statement.
Initial reports in Spain suggest Varane could be out for up to six weeks, making him a serious doubt for the second leg of the Champions League last-16 tie with Napoli at the San Paolo.
Varane could also miss league games against Villarreal, Las Palmas, Eibar, Real Betis, Athletic Bilbao and Leganes, though Madrid will at least hope to have him fit for the derby with Atletico Madrid on April 9.