The Gunners take on Chris Hughton's side on Sunday lunchtime just a couple days after their Europa League win over BATE Borisov in Belarus.
Despite that lengthy trip, Merson expects Arsene Wenger and co to claim a victory over the Seaguls.
But the Arsenal great has told Wenger that he must play his best team or they could slip up like Tottenham did in their recent draw with Swansea.
Merson told Sky Sports: “Arsenal's trip to Belarus in the Europa League should not get in the way of three points against Brighton.
“However Arsene Wenger can't take underestimate Chris Hughton's side.
“That's where some managers are coming unstuck at the moment, taking teams lightly.
“We saw that when Tottenham played Swansea at Wembley with Heung-min Son playing left wing-back and Liverpool making six changes against Burnley.
“You have to play your best team and if they do the Gunners should win easily.”
Merson does not expect Tottenham to make any mistakes when they take on Huddersfield tomorrow.
He added: “Huddersfield have been tight at the back so far, keeping four clean sheets from their six league games so far, but sooner or later they are going to have to come out and score goals.
“I watched them against Burnley last week and I thought they were very comfortable but at some point they are going to have to do a bit more because I don't think another 30 0-0 draws will get you out of trouble.
“Huddersfield are coming up against a different kettle of fish this weekend but they do work hard and that will shock Spurs, but in the end the visitor's quality will tell.
“Harry Kane is absolutely flying at the moment and Huddersfield won't have come up against anyone like that yet. I don't see how they will be able to contain him.”
