He began playing soccer in the Serbian League East, and was part of the youth system of his home town team Dubočica Leskovac before coming to the United States in 2005.

More than a month later he made his debut in the league for Toronto on October 16, 2010 versus Columbus Crew in a 2–2 home draw after teammate Jon Conway was shown a red card in the 72nd minute.

Kocić made his 2011 season debut on July 27 under Aron Winter in a 2–1 home victory over Real Esteli during Champions League play.

Kocić started in the return leg with a stand out performance, a week later Frei sustained a broken fibula during training requiring surgery expected to keep him out for six months.

[16] Kocić, along with Ryan Johnson, was traded to the Portland Timbers on December 12, 2012 for the third overall selection in the 2013 MLS SuperDraft, Joe Bendik and allocation money.

"With the addition of Miloš, we felt it was important to add another experienced goalkeeper to strengthen our depth in that position," said Timbers technical director Gavin Wilkinson.