Ljajic completes Fiorentina move
The 18-year-old Serbian signed for the Red Devils in January 2009 along with Belgrade team-mate Zoran Tosic, with Ljajic remaining at Partizan on loan last year before being expected to join Sir Alex Ferguson's side this month.
However, with no guarantee of a work permit for the playmaker, United opted to pull out of the deal.
"Partizan president Dragan Djuric and general secretary Darko Grubor negotiated the deal in Florence and Ljajic will sign for Fiorentina as soon as he passes Thursday's medical," the Serbian champions said.
"We wish him all the best after he came through the ranks at Partizan, where he scored 13 goals in 70 first team matches."
Ljajic has been a regular for Serbia's under-19 team and has made two appearances for the under-21 side in qualifiers for next year's European Championship in Denmark.
Instead of joining compatriots Nemanja Vidic and Zoran Tosic at United, Ljajic will link up with Montenegro striker Stevan Jovetic, his former Partizan team-mate.