Arsenal have revealed that midfielder Lucas Torreira suffered a fractured ankle during the FA Cup fifth-round win over Portsmouth on Monday.
The Uruguayan international was carried off on a stretcher during the first half at Fratton Park after a challenge involving Pompey defender James Bolton.
The Gunners have not put a timeline on Torreira's return and say they are "awaiting further specialist reviews which will determine (a) recovery plan."
Torreira has made 33 appearances for Arsenal this season, scoring two goals.
Meanwhile, defender Kieran Tierney is back in full training after recovering from a dislocated shoulder.
The Scotland international has only made 11 appearances since his summer move from Celtic due to injuries.
Cedric Soares will return to full training next week after recovering from a knee injury while Sead Kolasinac should resume training by the end of the month after a shoulder problem.
Calum Chambers will start his rehabilitation process on a ruptured anterior cruciate ligament injury to his left knee.
The timeframe for his return is between six and nine months.
