It is feared the Chile international could be out for some time, although Arsenal do have the international break to assess his condition.
Arsenal were also without playmaker Mesut Ozil for the clash, with the German currently nursing a hamstring problem.
We face big problems to regroup and find resources to sort out the problem
Wenger on Sanchez's injury
And Wenger admits he is worried he does not have adequate cover for Sanchez.
“We lost Alexis Sanchez in the second half, he was very dangerous in the first,” Wenger said.
“He came out in the second half and he couldn’t move any more. In the first half he was a guy who created a lot.
"It leaves us in a unique situation that we’ve never had before. We face big problems to regroup and find resources to sort out the problem. We need some togetherness.”
REUTERS
Alexis Sanchez was injured in Arsenal's loss at West Brom
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GETTY
Arsenal were outplayed at the set piece against West Brom today
REUTERS
Petr Cech (left) was also injured in the West Brom defeat
Arsenal face Manchester City after the international break - a crunch tie if they want to finish in the top four this season.
And Wenger admits he is wary about the clash to come.
"We face some serious challenges. The City game at home is a big game for us."
