Macheda looked to be the 'next Ronaldo' as he scored an incredible winning goal against Aston Villa at the age of 17 in 2009.
The Italian spent several seasons on the fringes of Sir Alex Ferguson's United squad, but once it became clear he was not in the manager's plans, after several loans he joined Cardiff on a free transfer.
The 27-year-old also spent time in Italy, for Serie B side Novara.
Now he moves to Panathinaikos as a free agent on a three-year deal as he looks to put his career back on track.