Tosic was signed by Sir Alex Ferguson for £7m in 2009 but after just five appearances at Old Trafford, he moved to CSKA Moscow.
However, speaking ahead of Serbia's match against Scotland, Tosic revealed that he still looks back to his time at Manchester United and thinks that he should have stayed longer at the club after he had returned from a loan spell at Cologne.
Tosic told the Daily Record: "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."
Tosic has scored seven goals in 42 appearances for Serbia.