Arsenal manager Mikel Arteta has confirmed that Willian was substituted midway through the Leeds United game with an injury.
The Brazilian started on the right wing for the Gunners at Elland Road, but he was brought off at the half-time interval.
It was initially suggested that Willian was replaced by Reiss Nelson due to tactical reasons, but does not appear the case.
Speaking after the goalless draw, Arteta told: “He was feeling something muscular and we had to take him off.”
Meanwhile, the Gunners boss also confirmed that Bukayo Saka was in pain after a challenge late in the game and will be assessed.
The north London giants were made to work hard for the 0-0 draw after Nicolas Pepe was sent off after just 52 minutes for violent conduct.
They are currently 11th on the table with 13 points, seven adrift of fierce rivals Tottenham Hotspur, who are top of the standings.
Arsenal will face Molde in the Europa League on Thursday night.