Gabriel Martinelli was a late withdrawal from the starting XI against Newcastle after appearing to injure his ankle during the warm-up.
Mikel Arteta explained the latest with the Brazilian forward when he faced the media after the game.
"I am gutted. I was in my office before the game and one of the coaches came in and told me that Gabi had hurt himself, that he'd twisted his ankle.
"I went to the medical room and he was in tears. He was in a lot of pain and we're going to have to see how he is. It didn't look good. He was in pain so I imagine that we're not going to have good news with him."
Arteta added that he should be going for a scan on Sunday.
"We really want to know what's going on. He's a character and he wants to play the next game. He doesn't care and can handle pain but I don't know. Hopefully there is nothing too serious but to start with, it didn't look too good."
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