The Brazilian international was withdrawn midway through the second half of the 6-0 win at Bramall Lane.
After the game, manager Mikel Arteta played down the seriousness of the problem, stating it was only a “slight cut”.
However, Martinelli missed the Gunners’ next two fixtures against Brentford and Porto. He also withdrew from Brazil’s squad, suggesting it will be touch and go whether he will be back after the international break.
