Chelsea manager Jose Mourinho says Diego Costa did not start his side's opening Champions draw with Schalke because the striker was not fit enough.
Mourinho's side laboured to a 1-1 draw at Stamford Bridge on Wednesday, but wasted several clear chances to kill the game off.
Despite scoring seven goals in his first four games for the club, Costa was only named as a substitute as Mourinho opted to start Didier Drogba instead.
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"Costa has a problem," Mourinho said of his striker. "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.
"It was not to protect for the game Sunday [at Manchester City], it was because today he was not in condition to start the game."
Costa replaced Drogba shortly after Schalke equalised through Klaas Jan Huntelaar, but the Spaniard failed to make an impact.
The forward sparked fears after he withdrew from the Spain squad to face Macedonia in the recent international break, citing a hamstring injury.
Mourinho, however, quashed worries over Costa's fitness before the striker returned to score a hat trick against Swansea last weekend.
Now though, the Blues manager says midweek games will be a rarity for the 25-year-old.
"He played here one match and he was perfect," Mourinho said. "He went to the national team and after the game against France he came back to us injured. He came to us [from Atletico] and he was completely fine. He had a problem again in the national team, not with us.
"Now we have the problem and now we have to resolve the problem the best we can. Today 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. If today he starts the game, for sure he cannot play on Sunday. We have to go step by step."
Drogba deputised for Costa on his first Champions League appearance for Chelsea since scoring the decisive penalty in the 2012 European Cup win.
The Ivory Coast striker was unable to convert passes from Willian and Hazard, but Mourinho refused to be critical of the 36-year-old.
"He had a positive game," Mourinho said. "I'm not disappointed with the striker because of one inch, he scores a goal or doesn't score a goal. I am happy with what he did. If he scores that goal in this moment we're speaking about 2-0, not 1-1. We had very good chances to score the 2-0 and we didn't.
Schalke were severely depleted by injury and reeling from their worst Bundesliga start in more than 40 years. It appeared Chelsea would run amok after a scintillating start, with Eden Hazard to the fore.
Instead Chelsea failed to take their chances, with Didier Drogba among those culpable, and Mourinho was left to rue defensive lapses as Schalke equalised and held on for a point.
It appeared Huntelaar had fouled Fabregas in the build-up to the goal -- the Spain midfielder had appeared to have tackled Max Meyer late in the move which led to his goal -- but Mourinho had no complaints.
"From my position I can't say that [it was a foul]," 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 Draxler wants to come inside for his right foot and in a situation inside the box we have to press his right foot. It was also a mistake in the box.
"After that situation only one team tried to win and only one team had so many chances to win the game in a short period of time. In the last 15 minutes Remy could score, John Terry could score, Hazard could score.
"We had so many great situations. Again, that's football. To defend like they did is also football. A good point for them. Not a fantastic point for us, but a point."
Schalke boss Jens Keller was thrilled with his side's display. "I'm very, very proud of what my team did here against such a top team," he said. "Tactically we did exactly how we had planned. We were aggressive, we played right into space. We had really good tempo with Draxler and Sidney Sam. I'm absolutely delighted with the performance we gave here today."