Lucas Torreira was substituted at half-time during Saturday's draw with Crystal Palace.
Our diminutive midfielder has been at his tenacious best recently, winning our December Player of the Month award, but was replaced by Matteo Guendouzi after just 45 minutes at Selhurst Park.
So why did Mikel Arteta bring the Uruguayan off?
"Matteo was really good when he came on as well, but Lucas has been in good form," our head coach said. "He's given us a lot but I had to get him off because he wasn't feeling good.
"It's a muscle injury. We'll have to assess it with the doctors tomorrow. We will know more the day after."
Copyright 2020 The Arsenal Football Club plc. Permission to use quotations from this article is granted subject to appropriate credit being given to www.arsenal.com as the source.