Arsenal forward Alexis Sanchez's right ankle is in "an absolutely terrible state" and he may have ligament damage, says manager Arsene Wenger.
The Chile international was substituted with 12 minutes left of Saturday's 3-1 defeat by West Brom.
Sanchez was injured in the first half, when he was fouled by James McClean.
"He should not have played in the second half but he insisted that he wanted to," Wenger said. "In the end we had to take him off."
Arsenal's next match is at home to Manchester City in the league on 2 April, but Sanchez is in Chile's squad for World Cup qualifiers against Argentina and Venezuela, the first of which is on Thursday.