Arsenal won the second leg but lost on away goal 3-3 aggregate against Monaco in the Champions League.
Manchester City’s title defense was dealt a further blow Saturday with a first loss to Burnley in 41 years.
One of their own, Welbeck came back to haunt United as he fired the winner on Monday at Old Trafford.
It was a night of upsets as two top teams were edged out in Champions League first leg.
Alex Oxlade-Chamberlain, however, will be out for another two weeks and Wenger had no date for the return of Jack Wilshere.
Lampard’s decision to stay with Manchester City has “outraged” fans of New York City FC.
Arsenal hang on to win in a tense finish after Giroud’s red card, remain within touching distance of top 4.
Despite failing to secure all 3 points, Arsenal moved back into sixth spot with 27 points from 17 games.
Wenger, who has reputation for keeping his powder dry in transfer, said there was no need for reinforcements.
Club officials blocked unhappy supporters from displaying banners calling for Wenger to be sacked.
Arsenal will also miss the services of Theo Walcott, who is still recovering from a thigh injury.
After a 3-0 defeat against Manchester City on Sunday, Southampton travel to Arsenal on Tuesday.
Welbeck powerful header in the 66th minute gave the Gunners the much needed three points.
Captain Mikel Arteta and striker Yaya Sanogo are the latest names on a growing injury list.
Arsenal beat Dortmund 2-0 to leave struggles behind, seal knockout passage in CL.