Arsenal midfielder Lucas Torreira was taken off the pitch on a stretcher in Monday's FA Cup fifth-round tie at Portsmouth.
Torreira, 24, came down holding his right leg after a tackle from Pompey defender James Bolton in the 12th minute at Fratton Park.
Arsenal head coach Mikel Arteta opted to replace the Uruguay international with Dani Ceballos, who is on loan from Real Madrid.
Torreira was helped on to a stretcher by the Arsenal medical staff and given oxygen.
Following Arsenal's 2-0 win, Arteta said: "Lucas was very sore and is in a brace. He will be assessed in a few days and then we will know more."
The Gunners eased through thanks to goals from Sokratis Papastathopoulos and Eddie Nketiah to send them into the FA Cup quarter-finals.
Torreira, who was signed from Sampdoria in 2018, has featured 32 times for Arsenal this season, scoring twice.