The Gunners were originally due to host United at Emirates Stadium on Saturday, May 6, but the match will now be televised live on Sky Sports on Sunday, May 4 at 4:00pm.
The clash could go a long way to deciding which of the two teams has a better chance of qualifying for the Champions League with Jose Mourinho and Arsene Wenger's sides lying fifth and sixth in the league respectively.
Both United and Arsenal have two games in hand over fourth-placed Liverpool heading into this weekend's action, with the Red Devils hosting West Brom on the Saturday before their neighbours Manchester City head to north London on Sunday to take on the Gunners.
Arsenal's meeting with United in May is set for gameweek 36, meaning the potential losers of the match have little time left to gain ground in the race for the top four.
A last-gasp goal from Olivier Giroud rescued a 1-1 draw in the reverse fixture last season, with Mourinho's men suffering the familiar fate of a home draw in a frustrating season at Old Trafford.