Arsenal and Unai Emery confirmed Welbeck would have X-rays on his leg after appearing to break his ankle.
Welbeck landed awkwardly after leaping in the air to meet a cross just after the half hour mark against Sporting, and needed oxgyen before being stretchered off the pitch.
Arsenal are now fearing the worst as Emery issued an update after the 0-0 draw with Sporting.
He has been taking to hospital. We are going to wait, Emery said.
The worst news tonight is these injuries – we think serious injury. I think Danny was working well.
His injury was hard for the mentality of the players because they looked at the injury. But when you are playing football in competitive matches it can happen.
He added: Its his ankle. He broken something in his ankle.
Welbeck was making his sixth start under Emery this season and was being linked with a January move.
The 27-year-old is out of contract at the end of the season and Emery admitted it was a major blow for Welbeck.
He said: He is a very good person, his commitment with us is very big. He helps us with his quality and capacity. This injury is very big for him, for us and for all.
Arsenal also lost Stephan Lichtsteiner to injury late in the game as the full-back appeared to pull his hamstring.