The Chile international was substituted for Alex Iwobi in the Gunners' 3-1 loss on Saturday and the manager confirmed it was for a nasty injury
Alexis Sanchez suffered an ankle injury during Arsenal's 3-1 defeat at West Brom, manager Arsene Wenger has confirmed.
Sanchez equalised after Craig Dawson's 12th-minute opener but substitute Hal Robson-Kanu made an instant impact 10 minutes after half-time and Dawson headed a second to ramp up further pressure on the beleaguered Wenger.
Fan protests, both with banners in the away end at The Hawthorns and on the back of a light aircraft circling the ground - a rival plane had a message of support for Wenger - were again a feature as the 67-year-old lost his top scorer during Arsenal's fourth defeat in five Premier League games.