Arsenal have now won four matches in a row in all competitions, with Emile Smith Rowe and Pierre-Emerick Aubameyang completing the 2-0 extra time win over Newcastle.
In his post-match press conference, Arteta was pessimistic about Martinelli’s injury.
“I am gutted,” Arteta said. “I was in my office before the game and one of the medical staff came in and said he twisted his ankle.
“He was in tears and in a lot of pain. We’re going to see how he is but he didn’t look good.