Teenager Martinelli started his first game since March against City on Tuesday after returning from a knee injury.
The forward tried to carry on following half-time, but he had to come off a few minutes after the break.
Arteta, however, is hopeful the injury is not too serious, with Arsenal facing a busy run of games – starting with their Boxing Day clash against Chelsea.
“I was really happy with Gabi,” said Arteta. “He looked really sharp in training.
“He looked as he always is, with his energy and the passion that he has. He was really good but he picked up a really bad kick on his shin and he had to come off, because he wasn’t comfortable carrying on playing.”
Asked by Arsenal’s official club website how serious it was, Arteta replied: “I don’t think it will be too serious.
“But he will need a couple of days. I am really pleased with another young player’s performance as well.”