Tosic arrived at the club in 2009, costing the club around £7million, but after just five appearances for the club he was on a flight to CSKA Moscow and never heard of again, until now.
As the Serbian international side prepare to take on Scotland, Tosic admits that his time with United is never far from his mind and believes that he maybe should have stayed.
Speaking to the Daily Record, the Serb said: "When I came back to Manchester, I was expecting to play more games for United but it didn't happen.
"In the end I wasn't sure I was going to get the chance I felt I deserved so decided to change club. Even now I am always thinking about that moment. Maybe I shouldn't have been so quick and should have worked longer to show Sir Alex.
"Maybe I should have stayed and fought for my place. This was Man United after all."