"There is no fracture in Thomas's leg but his injury still has to be assessed," manager Arsene Wenger told the club website on Thursday.
"There is still a good chance he will not play on Sunday."
The Belgian international has made a huge impact at the Emirates since his move from Ajax Amsterdam last year, scoring on his league debut at Everton. He has netted six goals in 31 appearances for the club.
If Vermaelen is ruled out, veteran defender Sol Campbell could be called into action for the third time in a week.
Wenger said Croatia striker Eduardo, who also limped off in Wednesday's goalless draw at Villa Park, will miss Sunday's match but could be back for the visit to Chelsea the following weekend.
"Eduardo has a small, small, small hamstring (injury). He will be out for one week. He will not make Man United but he might make Chelsea," said the Frenchman.
Arsenal are third in the league, a point behind United and two adrift of Chelsea, who have a game in hand.
Wenger also has Ivory Coast defender Emmanuel Eboue and Cameroon midfielder Alex Song back at his disposal after they returned from the African Nations Cup in Angola.
