The Gunners received plenty of plaudits for their performance in Sunday’s 4-2 victory over Tottenham Hotspur in the north London derby.
Arsenal broke the deadlock in the first half thanks to Pierre-Emerick Aubameyang’s opening goal from the penalty spot.
However, Dele Alli and Harry Kane scored against the run of play to leave Tottenham with a 2-1 half-time lead.
Unai Emery opted to bring on Aaron Ramsey and Alexandre Lacazette at half-time and the substitutes had a big impact on the derby clash.
Ramsey created goals for Aubameyang and Lacazette before Lucas Torreira polished off a thrilling 4-2 win at The Emirates.
Manchester United were held to a 2-2 draw at Southampton on Saturday evening to extend their winless run to three games in the Premier League.
The Gunners have the chance to move 11 points ahead of Manchester United in the race to secure a top-four finish.
Former Arsenal midfielder Merson believes the Gunners will ease to a 2-1 victory over Manchester United at Old Trafford on Wednesday night.
“In the past we’ve seen Arsenal go to Old Trafford in form, play well but somehow still end up losing the game,” Merson told Sky Sports.
“However, unless Manchester United really pick their game up or the Gunners hit a brick wall after their efforts against Tottenham, I just can’t see how United win. I really can’t!”
Merson added: “I hope Unai Emery plays the side that finished the game against Tottenham, playing two up front with Pierre-Emerick Aubameyang and Alexandre Lacazette because that will cause United all sorts of problems.
“When United got back to 2-2 at Southampton on Saturday there should have been only one winner. However, they just didn’t kick on and it was like they were grateful to be back level at 2-2. We’ve got to remember this a different Man Utd to the one we used to watch.
“It’s the same club but the players are nowhere near in the same calibre. That’s the problem and that’s something we have to keep reminding ourselves. This is not the United of old and if they somehow managed to get in the top four they’d be pulling up trees.”
Arsenal are in fourth place in the Premier League table and eight points ahead of Manchester United, who are languishing in seventh spot.
The Gunners lost 2-1 to Manchester United at Old Trafford last term after Marouane Fellaini netted a 90th minute winner.
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