Born in Kruševac, Zajić came through the youth system at his hometown club Napredak, making his senior debut in 1998.

While with the Vitezovi, Zajić made 110 league appearances and scored 10 goals, before leaving due to the club's financial problems in the 2006 winter transfer window.

[1] He scored a brace in a 4–2 home victory over Groningen in the first leg of the UEFA Cup first round on 14 September 2006.

[3] In the following years, Zajić became one of the team's most important players, making 170 competitive appearances and scoring 37 goals.

[6] Zajić played one match for the Serbia and Montenegro national team at the 2004 Kirin Cup against Slovakia.