Career
He was born in Darda. Playing career
Grnja played in the North American Soccer League for the Toronto Metros-Croatia and the Tampa Bay Rowdies. Coaching career
Grnja has managed Croatian club side NK Osijek on two occasions - in 1991, and between 1993 and 1994.
Grnja also managed the Croatia under-21 side in 2005, and the under-19 side in 2008.