He's Serbian. City had a Montengrin center-back, Stefan Savic, who they traded as part of the deal to bring Nastasic to City.
Sidenote, if Yugoslavia was still together (yes I know, impossible), it'd probably be one of the top 5 teams at this tournament.
If you had Yugo instead of Bosnia, they'd definitely be a threat to go deep in the tourney. I'm sure I left off some legit guys, but this is some serious talent just from quick scanning the national teams of Bosnia, Serbia, Croatia, Slovenia, Montenegro, Macedonia, and Kosovo. Had to leave off guys like Olic who are playing well just because of their age.
1. GK Asmir Begovic (Bosnia - Stoke City)
2. GK Samir Handanovic (Slovenia - Inter)
3. GK Danijel Subasic (Croatia - Monaco)
4. DF Emir Spahic (Bosnia - 1899 Hoffenheim)
5. DF Branislav Ivanovic (Serbia - Chelsea)
6. DF Aleksandr Kolarov (Serbia - Manchester City)
7. DF Dejan Lovgren (Croatia - Southampton)
8. DF Vedran Corluka (Croatia - Lokomotiv)
9. DF Milso Brecko (Slovenia - Cologne)
10. DF Matija Nastasić (Serbia - Manchester City)
11. MF David Babunski (Macedonia - Barca B) (just to have a single Macedonian)
12. MF Enis Alushi (Kosovo - Kaiserlautern) (just to have a single Kosovar)
13. MF Sejad Salihovic (Bosnia - 1899 Hoffenheim)
14. MF Zoran Tosic (Serbia - CSKA Moscow)
15. MF Miralem Pjanic (Bosnia - Roma)
16. MF Nemanja Matic (Serbia - Chelsea)
17. MF Senad Lusic (Bosnia - Lazio)
18. MF Luka Modric (Croatia - Real Madrid)
19. MF Valter Birsa (Slovenia -Inter)
20. FW Stevan Jovetic (Montenegro - Manchester City)
21. FW Mario Mandzukic (Croatia - Bayern)
22. FW Vedad Ibisevic (Bosnia - Stuttgart)
23. FW Edin Dzeko (Bosnia - Manchester City)