Merson feels Arsenal have already dropped too many points this season.
“If they lose this they go seven points behind them,” he told Sky Sports News.
“I don't see Man City not beating Southampton, so that would be seven and six points behind their two biggest rivals for the title.
“That's a lot of points, especially the way these teams are winning football matches. They beat lesser teams with ease and the gulf is massive at the moment.
“I'd be shocked. If Arsenal lost this and went on and won the league I'd be absolutely amazed. I would be flabbergasted.
“They're not just chasing one team down, but chasing two.
“All of this about how there will still be 29 games to go - Arsenal will be out the title (if they lose).
“I just can't see how Arsenal will catch that up (a seven-point deficit) with the figures Man City have put up over the last five to six years.”