Martinelli only made his return from a long-term injury in the weekend’s defeat against Everton and was making his first start since March in the meeting with Pep Guardiola’s side.
He had looked Arsenal’s best player in the opening 45 minutes and set-up Alexandre Lacazette’s equaliser after Gabriel Jesus had headed the visitors in front early on.
The 19-year-old’s evening looked to be over when he was clattered by City goalkeeper Zack Steffen shortly before the break, and immediately went down clutching his ankle, but after receiving treatment he soldiered on to half-time, despite barely being able to break into a jog.
It was a surprise then when Martinelli re-emerged for the second half, but after only three minutes he went down again and this time limped off for the final time as Nicolas Pepe was sent on in his place.
Mikel Arteta will hope desperately that the injury proves nothing too serious, with the youngsters return having given the confidence-shot Gunners some much-needed confidence amid their Premier League struggles.