The 22-year-old joined Roma from the Spanish club in July last year, but he has now completed a short-term move to Milan.
"Until a few years ago I never thought about playing for a team other than Barca, I could not even imagine being with another club," he told Gazzetta TV.
"I arrived there when I was just nine years old, I came up through the youth ranks, I was with Barca for 12 years and I thought that I would stay there forever. Then I had the opportunity to move to Italy and I thank God for letting that happen.
"Rome has opened up another world, I met a completely different reality, from a football and more personal perspective, and this can only be a very good thing for my career."
Bojan could make his San Siro debut against Atalanta on Saturday.