Chelsea's Brazil playmaker Oscar was taken to hospital after being clattered by Arsenal goalkeeper David Ospina during the 0-0 Premier League draw at the Emirates on Sunday.
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Oscar was played in by Cesc Fabregas in the 16th minute of the London derby and after dinking the ball over the outrushing Ospina he was flattened, appearing to be struck on the head.
After treatment he was able to play on, but did not appear for the second half and was replaced by Didier Drogba.
Chelsea manager Jose Mourinho refused to criticise referee Michael Oliver for not giving a penalty.
"He went to the hospital at halftime," Mourinho told reporters.
"We are waiting. We don't know yet (if it's concussion)."
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