Martinelli was forced out of their FA Cup defeat of Newcastle United in the warm-up with an ankle injury.
"He had really bad luck, said Arteta.
"We didn't look after the game because he was in a lot of pain. Yesterday he tested a little bit better so let's hope we have a scan today and it is not as serious and we can have Gabi back really soon.
"I was gutted for him."
“The next two games are crucial to see the direction we are taking to reinforce the things we have improved on," said Arteta.
"The results we have had recently. We will know much more in the next two games."
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