Sanchez scored Arsenal’s only goal in the first half but in the 43rd minute was on the receiving end of a scything tackle from James McClean, for which the West Brom winger was booked.
Though he continued on through the injury Sanchez was in obvious discomfort and after struggling to influence the game as West Brom dominated Arsenal in the air he was withdrawn on 78 minutes for Alex Iwobi.
Arsenal fans responded to the decision by chanting “you don’t know what you’re doing” to the manager but Wenger made clear that, if it had been up to him, Sanchez would not have come back out for the second half.
“He was injured from the tackle in the first half,” Wenger said. “It’s a bad tackle. His ankle is in a terrible state.
“He should not have played in the second half. He insisted that he wanted to come out.
“In the first half he was the one who created the chances, many dangerous situations, and you could see in the second half he couldn’t anymore. In the end we had to take him off but he should not have even played.”
Sanchez’s injury comes with Arsenal out of action for the next fortnight and Wenger will hope he has recovered in sufficient time for the visit of Manchester City to the Emirates on April 2.
Before then Sanchez is due to join up with the Chilean national team for crucial World Cup qualifiers in Argentina and against Venezuela.
The 28-year-old played for Chile in November against Wenger’s wishes – he labelled the decision “suicidal – and the Arsenal manager admitted he could not control whether Sanchez would be part of Juan Antonio Pizzi’s squad.
“Chile goes to Argentina for a massive game but it’s not until next week,” Wenger told Standard Sport. “If it’s only a kick he will play.
“His ankle is swollen. If the ligament is damaged he will not play.”