Arsenal boss Unai Emery revealed after the match that the club fear Welbeck has sustained a "very big injury" to his ankle.
The injury comes as a huge blow to Arsenal and Welbeck, who has struggled for fitness since leaving United for the Emirates Stadium in 2014.
Welbeck, a product of United's youth system, has since received well wishes from the Red Devils, and also former team-mates Jesse Lingard and Ashley Young.
United posted on their official Twitter account on Friday morning: "Wishing @DannyWelbeck a full recovery from his injury. #MUFC"
While Lingard - another United academy graduate - wrote on his Twitter account: "Welbz Get Well Soon Brother @DannyWelbeck."
WelbzGet Well Soon Brother@DannyWelbeck— Jesse Lingard (@JesseLingard) November 8, 2018
Welbeck's injury overshadowed the point which secured Arsenal's place in the knockout phase of the Europa League with two games to spare.
The 27-year-old landed badly on his right ankle after attempting to win a header in the 25th minute.
Welbeck later received oxygen and had his leg in a protective brace as he was stretchered off the pitch and taken to hospital.
Young, who played alongside Welbeck at United between 2011 and 2014, wrote on Twitter: "Absolutely gutted for you Welbz! Come back better and stronger bro @DannyWelbeck."
Absolutely gutted for you Welbz !— Ashley Young (@youngy18) November 9, 2018
Come back better and stronger bro@DannyWelbeck
While Welbeck's England team-mate Marcus Rashford also wrote: "Wishing you a speedy recovery Welbz."
Wishing you a speedy recovery Welbzpic.twitter.com/e94tXdeJC9— Marcus Rashford (@MarcusRashford) November 9, 2018
Welbeck has scored five goals and registered one assist in all competitions for Arsenal so far this term.