The two deadline day signings capped off a terrific transfer window for the Gunners.
And Merson thinks their abilities will allow Emery to be flexible with his defence.
"When you're looking at them and you're naming them players, I wouldn't be surprised if he started going to a three at the back," Merson said on The Debate.
"Play them two and David Luiz in the middle of them. He can come out and play, you've got Tierney playing as one wing-back.
"Very much [that suits Luiz], I think it suits all of the defenders.
"If you have three centre-halves playing there it gives all of them something to fall back on.
"If Tierney can get forward he can play, so he'll want to get forward.
"They'll want to bomb forward down the other side and they can score goals.
"I'm looking forward to Arsenal this season. I was quite impressed [against Newcastle], I was quite impressed.
"It was a hard game, going to Newcastle, first game of the season, a couple of new players.
"For me it was comfortable and [Pierre-Emerick] Aubameyang what a goal, what a goal."