Perez was injured in Arsenal’s 2-0 win overReading (EFL) Cup on Tuesday, October 25.
The striker limped off his the second half of the Round of 16 EFL Cub game following a challenge from Danzell Gravenberch.
According to several reports, the 27-year-old has damaged his ankle ligaments and will likely be out for six weeks.
Arsenal have not put a timescale on his return, but the summer acquisition from Deportivo de La Coruna is likely to miss Gunners’ clashes against Sunderland, Ludogorets, Tottenham, Paris Saint-Germain,  ManchesterUnited, Bournemouth and Southampton.
Ahead of their Premier League trip to Sunderland, Arsenal are also sweating on the fitness of midfielder Santi Cazorla.
Cazorla got injured in Arsenal’s 6-0 drubbing of Ludogorets in the and missed their goalless home draw to Middleborough in the Premier League.