A large part of United's success this season has been the purchase of superstar striker Van Persie.
"I never thought we had a chance of getting Robin because I didn't think Arsenal would sell to us," said the manger on his striker, who has 22 goals this season.
"My discussions with Arsene were good but long, probably a couple of months. They realised that the lad wanted to leave. It was a matter of negotiating the price with Arsene."
United eventually paid £25million for the Dutchman.