Real Madrid are sweating on the injury news for winger Arjen Robben after he broke down during Sunday's league draw with Espanyol.
The Holland international lasted just 25 minutes after appearing as a half-time replacement before he himself had to be substituted with a hamstring problem.
Robben will now undergo further tests over the next few days to determine the extent of the injury and how long he is likely to be out for.
Madrid coach Bernd Schuster believes his side felt Robben's loss during the 2-2 draw against Espanyol, saying: "It's a pity he got injured because I'm sure that with him on the pitch things would have turned out better."
Schuster felt his side's second-half performance against Espanyol should have been enough to win them all three points against the visiting Catalan side.
Madrid were somewhat fortunate to be level at half-time against an impressive Espanyol having twice fallen behind in an opening period where their opponents also struck the woodwork.
The reigning champions looked much better after the break, but there was no way past Espanyol goalkeeper Carlos Kameni as the match remained 2-2, much to Schuster's frustration.
"We deserved to win in the second half. We were better and we had enough chances to have taken the victory," said Schuster
"Kameni made some very good saves and we were not accurate enough to score the third goal, but I think that in the second half we deserved more."
Madrid had plenty of efforts during the match, but many of them were from long range and rarely troubled Kameni.
Schuster did not take his players to task over that though, saying: "There's nothing bad about a player trying to score from outside the area, especially with shooters like (Rafael) Van der Vaart, (Gonzalo) Higuain or (Ruben) De La Red.
"It's true that the majority were off target, but that's another matter."
Madrid may not have managed to stretch their winning streak to seven matches on Sunday, but they did welcome back Wesley Sneijder.
Sneijder had been absent since suffering a knee injury during a pre-season match against Arsenal, but he re-appeared in the second half against Espanyol.
"The return of Sneijder is a positive, he has recovered very quickly," Schuster said.
"It's a shame because it wasn't the best game for him to come back in, entering with the score at 2-2 in the second half, looking for the win
"But I think that he was at a good level to help us. It's clear that it's his first day back, but when he improves his fitness with the (Holland) national team, he will be back to how he was before."