Real Madrid head coach Carlo Ancelotti has revealed that Ferland Mendy "felt a twinge in his leg" against Atletico Madrid on Wednesday, with the France international now seemingly facing a spell on the sidelines.
The 29-year-old has again been an important player for Los Blancos this season, featuring on 30 occasions in all competitions, including 11 outings in the Champions League, but he could potentially be out of the quarter-finals against Arsenal depending on the seriousness of the damage.
Ancelotti has said that Mendy will need to be assessed after suffering a muscular issue in the Madrid derby, which led to him being replaced in the latter stages of normal time.
"I think it's a muscle issue because he felt a twinge in his leg. They'll assess him in the next few days," Ancelotti told reporters.
The two teams could not be separated at the end of 120 minutes, with a 1-0 victory for Atletico on the night meaning that penalties were required, as the aggregate score was 2-2.
Real Madrid triumphed 4-2 in the shootout, and Ancelotti has praised his side for navigating their way through a tough tie.
"It was a difficult game, and even more so when you concede inside a minute. After that they dropped in to defend and looked to catch us out on the counter. The priority was to have effective possession of the ball and not complicate the game again. It was an evenly-matched tie and Atlético are one of the best in the world defensively," said the manager.
"They're well drilled, defend and work hard for each other, and we had a great chance through that incredible Kylian Mbappe move but we missed the penalty and it was level until the shootout. That's when we sent our best taker up first, and then Antonio Rudiger went last because he scored against [Manchester] City."
"I tried to explain our priority, which was not to complicate things by losing the ball in bad areas where they could catch you out of position. If they had made it 2-0, the game would have been very tough."
"We were better in that sense in the second half of extra-time. We always have to look to improve and work towards that. I've already explained what our approach was in this match. It looked like we needed to score a goal and we were never out of the tie at any point."
Vinicius Junior missed a penalty in the latter stages of the match and was then surprisingly withdrawn before the end of extra-time, with the Br azil international not taking part in the shootout.
The forward looked frustrated when he left the field, but Ancelotti has revealed that the South American had asked to be substituted.
"It was already decided Vini Jr. would take it and unfortunately he missed. He wasn't going to take one in the shootout but he asked me to come off because he was very tired," said the Italian.
Real Madrid will continue their La Liga campaign with a clash against Villarreal on Saturday evening, and they will then be back in action after the international break at home to Leganes on March 29.