Chelsea manager Jose Mourinho suggested striker Diego Costa is not yet ready to start more than one game a week.
Costa, who joined from Atletico Madrid for £32m in July, was named on the bench as the Blues drew 1-1 with Schalke in their Champions League Group G opener on Wednesday.
The 25-year-old, who has seven goals, suffered a hamstring injury while on international duty with Spain recently.
Mourinho said: “If he has one week to let the muscle recover he can start.”
Costa passed a late fitness test to play against Swansea on Saturday and he scored his first hat-trick in English football in a 4-2 win.
However, Mourinho opted to give striker Didier Drogba his first start since rejoining Chelsea in the summer, but the 36-year-old struggled to make an impact as Cesc Fabregas’s opener was cancelled out by Klaas-Jan Huntelaar.
Costa replaced Drogba in the 74th minute but could not force a winner.
Chelsea, who are top of the Premier League after taking 12 points from 12, travel to Manchester City on Sunday.
“It was not to protect Costa for the game Sunday [at Manchester City], it was because today he was not in condition to start the game,” added Mourinho.
“Playing on Saturday, three days is not enough for him to recover.”
Drogba’s appearance was his first for Chelsea in the Champions League since scoring the decisive penalty in the 2012 final against Bayern Munich.
However, he failed to make the most of an opportunity to put Chelsea 2-0 up when he was put through by Eden Hazard, dragging his shot just wide.
“I’m not disappointed with the striker because of one inch, he scores a goal or doesn’t score a goal,” said Mourinho.
“I am happy with what he did. If he scores that goal in this moment, we’re speaking about 2-0, not 1-1.”
After Huntelaar’s equaliser, Chelsea finished the stronger side but found the Schalke defence in inspired form, with substitute Loic Remy seeing a shot cleared off the line.
“After the 1-1 we had a fantastic reaction and chances to win the game, but that’s football, that’s Champions League, that’s normal,” said Mourinho.
“Congratulations to Schalke because they got their objective. There is a little bit of frustration for us, because we did everything to win and we could not.”