The Chile international had to be substituted shortly after half-time at The Hawthorns after suffering the problem in a heavy challenge in the first half.
Sanchez was Arsenal’s standout player in the first half and it was the Chilean who scored the Gunners’ equaliser before the break.
The news of Sanchez’s latest injury blow will come as a setback to the Gunners, and Wenger was quizzed about the forward’s ankle after the game ahead of the forthcoming international break.
Wenger told his post-match news conference at The Hawthorns: “He was injured from the tackle in the first half. It was a bad tackle. His ankle is in an absolutely terrible state. He should not have played in the second half but he insisted that he wanted to come out.
“In the first half he was the one who created many chances, made dangerous situations and in the second half you could see that he couldn’t anymore. In the end we had to take him off. He should not even have played in the second half.
“Chile goes to Argentina for a massive game but they play only next week and if it’s only a kick, he will play. If the ligament is damaged, he will not play.”
Next up for Arsenal in the Premier League is a crunch clash against Manchester City at The Emirates on 2 April as Wenger’s men look to get their top-four bid back on track.
The Gunners finished second and without a trophy last season.
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