The forward picked up a serious injury just short of the half-hour mark and was forced to leave the field on a stretcher
Arsenal suffered an injury blow during their Europa League tie against Sporting on Thursday as Danny Welbeck was forced to leave the pitch on a stretcher.
Welbeck, who scored the winning goal in the reverse fixture in Portugal, was replaced by Pierre-Emerick Aubameyang in the 29th minute of the game.
The Arsenal forward was challenging Sporting full-back Bruno Gaspar for a header when their legs tangled and Welbeck landed awkwardly on his ankle.
Welbeck was quickly surrounded by his team-mates, with Matteo Guendouzi visibly shocked by the incident, before receiving oxygen and being carried from the pitch.
The Gunners went into the tie knowing that a victory would see them qualify for the knockout stages of the competition, joining Premier League rivals Chelsea.
Maurizio Sarri's side claimed a narrow 1-0 victory in Belarus earlier in the evening, with Olivier Giroud scoring the only goal of the game.