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.
- EPL PHOTOS: Everton blank jittery Man Utd; Chelsea hold Arsenal
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)."
La Liga PHOTOS: Real Madrid go two points adrift of leaders Barca
GST Bill: 10 things to watch out for
Quake death toll in India rises to 66
Rupee falls 21 paise at 4-month low against USD in early trade