Unable to find space in the Partizan first team setup, he was sent out on loan to Serbian second division side FK Teleoptik from Zemun.

There, the young, left footed centre back made 21 appearances and caught the eye of Fiorentina sporting director at that time, Pantaleo Corvino, who signed him in a deal for €4 million.

[5] Nastasić spent some time in the Fiorentina youth side but, due to a lack of quality centre backs in the squad and suspensions and injuries, he trained with the first team on many occasions.

It was these qualities that led to a deadline day transfer to English side Manchester City in a move worth €24.4 million,[6] excluding the value of Stefan Savić who was given to Fiorentina as part of the exchange.

On 11 March 2015, Schalke 04 activated the transfer clause on his loan deal, believed to be €12 million, and Nastasić signed a four-year contract with the German club.

[19][20] In August 2021, Nastasić signed for Fiorentina again following Schalke 04's relegation from the Bundesliga as a replacement for Germán Pezzella, who moved to Real Betis Balompie the same week.

[25] Having represented Serbian youth football teams,[26] Nastasić made his debut for the senior squad on 29 February 2012 in a friendly match against Cyprus.