Lucas Torreira was sent off after twelve played minutes in Monday's fifth round of the FA Cup against Portsmouth.
Torreira was challenged for the ball by James Bolton in the 12th minute and he came down holding his right leg.
The Uruguay midfielder was seemingly in a lot of pain Arteta was forced to make his first change in the match replacing him with Dani Ceballos, who is on loan from Real Madrid.
Torreira was taken off on a stretcher by the medical staff and was given oxygen.
Arsenal are now without one of their most important players at the most crucial stage of the season.
However, Mikel Arteta gave an update on Torreira's injury after the game.
"Lucas was in a lot of pain and he will be absent for couple of days until we know more," said the head coach of Arsenal Mikel Arteta.
"We still don't know if it’s the bone or ligaments, but we must find out in few days."
Torreira just made his first start for Arsenal since the 2-2 draw against Chelsea at the end of January and he got injured.
Lucas Torreira was signed form Sampdoria in 2018 and this season he has featured 32 times for Arsenal and only scoring twice.