The winger played no part in the Gunners' 4-0 win over PSV Eindhoven in the Champions League on Wednesday, suggesting he might not feature against Tottenham.
Martinelli is a crucial part of Mikel Arteta's team and will almost certainly start if fit.
Is Martinelli fit to face Tottenham?
The 22-year-old started Arsenal's game against Everton earlier this month.
He saw a goal ruled out due to Eddie Nketiah being offside before leaving the pitch after just 24 minutes.
This was because of a hamstring problem.
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The Brazilian then played no part in Arsenal's Champions League win over PSV.
Since the game at Goodison Park, Martinelli has yet to train with the squad.
So with little time remaining until the match, it doesn't look good for the forward.
But Arteta refused to totally rule Martinelli out of contention.
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Speaking before the PSV match, he said: "He felt something in his hamstring and we need to do some further tests to assess if there is any big damage or not, but he will be out for tomorrow's [PSV Eindhoven] game, that's for sure.
"It's a possibility [to be fit for the derby], but we don't know yet.
"We need some more tests and see what happens."
Arteta then spoke to the press on Friday about Martinelli.
He said: "With Gabi we're still assessing him, so let's see if he can make the game or not."