Fernando Torres has been ruled out of Chelsea's Champions League game at home to Schalke on Wednesday and could miss the Blues' next few matches.
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Torres, 29, has been struggling with a thigh problem that he aggravated in training on Monday, having been substituted in the 62nd minute of Saturday's 2-0 defeat at Newcastle.
Manager Jose Mourinho confirmed he would be without the Spain striker with what he described at his prematch news conference as a "muscular" problem, and he is awaiting the results of a scan to determine the extent of the injury.
"Fernando we know is a muscular injury" he said. "We don’t know the dimension, we have to wait."
Should the results bring bad news for Chelsea, Torres could miss the rest of the club's November fixtures, which feature Premier League matches at home to West Brom and at West Ham as well as the Champions League trip to Basel.
One of either Samuel Eto'o or Demba Ba are expected to come into the side in place of Torres, who has five goals in all competitions to his name so far this season, most recently scoring a late winner in the 2-1 victory over Manchester City nine days ago.
"Samuel and Demba, they want to play, they want to play," Mourinho said. "They are waiting for opportunities to play so when they have that chance, and they know they are going to have it in this game and the next game against West Brom, they know they are going to have in their hands the job to play up front. I think it has to be, a good motivation for them and hopefully they can express on the pitch the way they work during the week."
Chelsea currently top Group E, after beating Schalke 3-0 in Germany in their last game, but Mourinho is taking nothing for granted as they look to book their place in the knockout phase.
"We are in a stable position to qualify in the Champions League but if we lose again we are in a difficult position, so Wednesday is an important game for us," he told the club's official website.