The 24 year-old Russian has revealed he had agreed terms with United last year, only to be blocked from making the move due to work permit difficulties.
"I was in shock, it was a dream transfer. The deal was done for around eighty percent, but I could not obtain a work permit with my limited number of caps for Russia," revealed Mamayev.
"Sir Alex Ferguson said he would try to solve it, but the transfer never came."
Mamayev has only two caps for Russia and says he first learned of Ferguson's interest from former United winger Zoran Tosic.