The Australian actor took up the sport to prepare for his film 'Real Steel' - an action movie set in the near-future where boxing is dominated by robots - and although he loves stepping inside the ring, Hugh believes his opponents took it easy on him because he's a celebrity.
He said: "I’ll absolutely know my career is over when I go in for a boxing session and get the s**t beaten out of me, and the other guy won’t care.”
However, one person who wasn't impressed by his fame was legendary pugilist Sugar Ray Leonard – who has won world titles in five different weight divisions – and Hugh believes he even went harder on him when the cameras were around.
He told Men’s Health UK magazine: "I was a little star-struck. He hit me harder than anyone, and if he saw a camera around, those punches became a lot harder."
Despite his punishing training schedule, Hugh loved the workout and even occasionally treated himself to a beer as a reward.
He said: "It involves strength and cardio. I don’t think there’s anything more tiring than boxing. It makes you feel amazing.
“I was about 10lb heavier than I normally would be. It was kind of nice to have a beer now and again.”
The full interview appears in the October issue of Men’s Health UK on sale now.