Arsenal slipped to another damaging defeat as goals from Craig Dawson and Hal Robson-Kanu condemned the Gunners to a fourth loss in five Premier League games.
The reverse leaves their hopes of making the top four slimmer than ever and manager Wenger’s future in more doubt.
Sanchez equalised Dawson’s opener but was subjected to a physical onslaught from the Baggies and limped off in the latter stages.
And Wenger revealed after the game that a particularly hefty challenge from James McClean at the end of the first half should’ve forced the Chilean out of the game entirely.
“It is a bad tackle. You see his ankle, he is in an absolutely terrible state and he should not have played in the second half,” he said.
“He insisted he wanted to come out. In the first half he was the one who created many dangerous situations but in the second half he couldn’t do any more and we had to take him off.”