Takehiro Tomiyasu left the Emirates on crutches following Arsenal's Europa League elimination in the hands of Sporting.
Tomiyasu was replaced by Ben White after barely 20 minutes and Mikel Arteta confirmed that injury could be serious.
He said: Tomiyasu looks pretty serious from his reaction and what he said to me.”
William Saliba also picked up a knock. Arteta added: "“Willy I don’t know, he had some discomfort and could not continue.”