Robert De Niro talked Sylvester Stallone into making 'Grudge Match'.

The veteran actors play long-time boxing rivals who square off once again 30 years after their last fight in the movie, and Stallone admits he was initially reluctant to make the film because he wanted to protect his legacy after starring in the iconic 'Rocky' movies.

He told Empire magazine: ''I had a great many reservations. He's relentless, don't let that quiet demeanour fool you. I was being precious about 'Rocky'. I was very happy with the way it ended. But Bobby just kept hammering away. Finally, he made sense. I talked to my wife and said, 'Maybe it would be interesting to take the good baggage and pit it against another iconic character because it'll never happen again.' ''

De Niro added: ''I was ready to go, but I knew the only way it would work was the two of us. I called him up and said, 'Let's try it.' ''

De Niro, who earned an Oscar for his portrayal of boxer Jake LaMotta in 1980's 'Raging Bull', admits he learned a lot more about boxing shooting this new film and even picked up tips from Stallone.

He said: ''I learned a lot more on this movie with the trainer I had, Robert Sale. I wish I'd had him back then. He's terrific, inspiring. Sylvester was great with that because he's had so much experience. I really learned a lot from him.''