The Gunners legend made the prediction after Danny Welbeck's sublime hat-trick in the Arsenal's 4-1 thrashing of Turkish side Galatasaray last night.
Merson, who made 289 appearances for Arsenal between 1985-97, slammed new United manager Louis van Gaal for selling the 24-year-old and insisted that he will score more than the man who replaced him at United, Radamel Falcao.
He told Sky Sports News: “For me, he is at the best club of his career with his runs and the service that he will get.
“I was shocked that he [Louis van Gaal] let him go. He wasn’t given a chance and always played right wing.
“He will score more goals than Falcao. I was shocked that he was allowed to go. A young English player.”
It's a bold and risky statement for Merson to make after just one game where Welbeck has looked a natural goalscorer. Whilst it's true Welbeck and Arsenal were very good last night, it's also true that Galatasaray's defence were beyond dreadful and they allowed the England international to run riot around them.
Both Welbeck and Falcao have had good starts at their new clubs, with the former taking his total to four goals in all competitions and the latter Colombian yet to open his account.
If Merson is referring to goals in all competitions then Welbeck has a huge advantage over the United man simply because he has Arsenal's Champions League campaign to fill his boots. In the Premier League on the other hand Welbeck has one goal and one assist in 256 minutes games, whereas Falcao has no goals but two assists in 160 minutes.
So it's pretty close at the moment; Falcao still has a lot to do in order to prove he will be a worthy investment for United, and Welbeck needs consistent performances to prove he is the born goalscorer that his huge potential promised.