Diego Costa is not yet ready to start more than one match in a week, Jose Mourinho revealed following Chelsea’s 1-1 draw with Schalke in the UEFA Champions League.
The £32million summer signing from Atletico Madrid has scored seven goals in four Premier League matches but was only available as a substitute for Chelsea’s opening Group G clash on Wednesday night.
Mourinho insisted Costa was not fit to start after scoring three times against Swansea last Saturday and ahead of Sunday's trip to Premier League champions Manchester City.
Costa limped out of last season's Champions League final againt Real Madrid with a hamstring problem and the injury recurred while on international duty earlier this month with Spain.
"Costa has a problem," Mourinho said. "He came to us (from Atletico) and he was completely fine. He had a problem again in the national team, not with us.
"If he has one week to let the muscle recover he can start a game. Playing on Saturday, three days is not enough for him to recover.
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"It was not to protect for the game Sunday, it was because he was not in condition to start the game. Now we have the problem and now we have to resolve the problem the best we can.
"He was not in condition to play. Sunday we believe he is. Next week against Bolton (in the Capital One Cup), for sure he isn't. We have to manage the situation until the moment he's completely fine."
Chelsea twice beat Schalke 3-0 in last season's competition but saw Cesc Fabregas' first-half goal cancelled out by Klaas-Jan Huntelaar.
Chelsea missed a host of opportunities while it appeared Huntelaar had fouled Fabregas in the build-up to the goal, but Mourinho's only complaints were with his side's defending.
"From my position I can't say that (it was a foul on Fabregas)," Mourinho said. "They scored 1-1 in a counter-attack situation. We made two mistakes.
"One was not to make a foul immediately when they recovered the ball and we had a chance for that.
"The other one was the fact I told my players 20 times (Julian) Draxler wants to come inside for his right foot. It was also a mistake in the box."
Mourinho felt the performance of Didier Drogba - playing for Chelsea in the Champions League for the first time since his penalty secured the trophy in 2012 - was "positive".
The Portuguese was frustrated to once again be asked about his choice of goalkeeper after continuing with Thibaut Courtois ahead of Petr Cech.
"I don't accept that you ask me about the goalkeeper every week," he added.
"For me it's just a decision and I can't say more than I say. What I say is that I have two fantastic goalkeepers, two of the best three goalkeepers in the world. And it's a fantastic situation for Chelsea."