Merson told Absolute Radio that if Van Persie had gone to Manchester City, the title would be returning to the Etihad.
"That's the thing, when Man United play poorly, they can still win football matches and for me, van Persie's probably been the difference this year.
"I think if Man City would've got van Persie I think they would've won the league. There's not a million miles between the teams, they just have a natural goal scorer in van Persie and Man City hasn't."
Merson also says Van Persie has actually improved since leaving Arsenal.
"Yeah, I mean he's gone, what is it, eight games now without a goal, which is a bit of a shock to be fair, I think they give the goal to Bramble but yeah, for me, I still think he's player of the year in my opinion, he's spread eagled the league, you know ten weeks ago."
Listen to Absolute Radio Rock n' Roll Football's Ian Wright every Saturday on 1215AM. For more, visit absoluteradio.co.uk/football.