Robert De Niro had to convince fellow veteran actor Sylvester Stallone to sign on for their new boxing movie Grudge Match as the Hollywood hardman feared the comedy would be mocking his Oscar-winning classic Rocky.

Stallone climbs back into the ring yet again in the new film, and he faces off with De Niro as rival fighters who come out of retirement to go toe-to-toe one last time.

De Niro relished the chance to play a boxer again following his Oscar-winning turn as Jake La Motta in 1980's Raging Bull, but Stallone was reluctant to join him as he suspected the movie would spoof his breakthrough film.

Stallone tells U.K. talk show host Graham Norton, "I was worried because it might have come out as unintentional comedy but the way they worked it and with the other cast it started to get good so I stopped being foolish, precious and protective of Rocky and let it go."

De Niro adds, "When I heard about it I always knew it had to be Sylvester to do it. I had to talk him into it - he had reservations, he was worried about it being a comedy but I said, 'Don't worry, we'll do it together and it will be okay'."