Januzaj left United over the summer for La Real.
He told the Daily Mail: "Jose had to make things happen very quickly and make quick decisions.
"I had not been playing for two years. He is a great manager and he has been fair to me because he let me leave to improve somewhere else. That's how the world goes and I look forward.
"I know Sir Alex is always at the end of the phone. The same with Giggsy (Ryan Giggs) and David (Moyes). Those people will always back me. My first job now is to impress here. I'm hoping for a World Cup place. The world does not stop."