The Arsenal manager reported that Sanchez's ankle was in "an absolutely terrible state" after he was taken off near the end of the 3-1 defeat but he is still unsure of the extent of the injury to his key attacker.
"He was injured from the tackle (from James McClean) in the first half. It was a bad tackle," Wenger said.
"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 end we had to take him off. He should not even have played in the second half."
Read the full article on eurosport.co.uk: Sanchez's ankle in 'terrible state' - Wenger