Arsenal boss Mikel Arteta explained substituting Thomas Partey during defeat to Aston Villa.
The Ghana midfielder pulled up in the second half and was replaced by Willian with 15 minutes left.
"He had a muscular injury so we had to take him off," said Arteta after the game. "He could not carry on playing.
"I don't know [how bad it is]," he added.
"We will see the extent of the injury. He wasn't feeling well enough to continue playing so we had to take him off."
