The Australian international arrived from Central Coast Mariners in January 2013, but a lack of first-team action saw him loaned out to Melbourne Victory at the start of 2014.
"Celtic has been a good experience but I won't lie, it has been tough," the 21-year-old told the Daily Record.
"I don't think I realised what a big club they are. The expectation on the players is just enormous.
"Some of these guys at Celtic have skill that would blow your mind. It was after two or three weeks that it dawned on me and I thought, 'This is hard. This is much tougher and sharper than back home'."
Rogic has made nine appearances for the Australian national team.