And the Gunners legend insists it would be “embarrassing” for either Unai Emery or Ole Gunnar Solskjaer to do otherwise.
Both clubs are in similar positions as they are chasing down a place in the top four.
Arsenal sit fifth and above United on just goal difference, but they are each only three points shy of Chelsea and seven off injury-ravaged Tottenham.
But with their FA Cup tie chosen for TV coverage on Friday night, it gives them extra time to rest and prepare for their return to Premier League action.
Arsenal host Cardiff on Tuesday while United welcome Burnley to Old Trafford the same night.
Neither fixture would be considered the toughest on their calendars, and Merson feels they should both be taking advantage tonight.
He is anticipating a goal fest in north London but believes Solskjaer’s Manchester United will just edge it 3-2 against his former club.
Merson wrote in his Sky Sports column: “What a game! Arsenal are like a bag of Revels though.
“I think United will just edge a cracker”
“This is a big game for both teams – both are likely to have a real go and have winnable fixtures in midweek so are not going to drop their star players for this one – it will be embarrassing if they do.
“Defensively both teams are poor but excellent going forward.
“I think United will just edge a cracker.”
Solskjaer has already revealed he intends to play Alexis Sanchez against his old side on his return from injury.
The £500,000-a-week forward has flopped at Old Trafford since joining from Arsenal last January.
But he is expected to be part of a strong United team at the Emirates, minus rested goalkeeper David de Gea who has not travelled and will be deputised by Sergio Romero.
Arsenal, meanwhile, are also due to put out their strongest available side.