But Tosic has failed to win a first-team place since, making only two appearances this season, in the Carling Cup against Barnsley and Tottenham.
However, he said: "I don't believe I have had my final say at United."
He added: "Hopefully my displays with Cologne will be my ticket back to Old Trafford."
Really think he should be given a chance, hopefully he will inspire at Cologne and be back rorythereddevil Ljajic left the club only last month after manager Sir Alex Ferguson decided not to take up the option to sign him.
He has since gone on to join Italian club Fiorentina.
Tosic and Ljajic are still regarded as two of Serbia's brightest young talents, despite their failure to settle in at the Premier League champions.