Sylvester Stallone took "two years" to be convinced to star in 'Creed'.

Sylvester Stallone

Sylvester Stallone

Stallone was unsure about going back to his most famous role as boxer Rocky Balboa for a seventh film in the 'Rocky' franchise despite being intrigued by director Ryan Coogler's plot for the movie, which sees an aged and sick Rocky train Adonis 'Donnie' Johnson, the illegitimate son of his late friend and former opponent Apollo Creed.

He explained: "It took (Coogler) about two years to convince me. I had been very, very grateful the way last chapter of 'Rocky Balboa' wrapped up his story in a satisfactory way for the audience. When Rocky waves goodbye, that was a goodbye to the audience and a thank you. I just thought, 'Finally.' And thought it was a wonderful send-off. Rocky stayed dormant for six or seven years, and then this fellow comes in, and says, 'Oh, can we dig him up?' I go, 'No, no, no, no.'

"Then he proceeded to tell me this story. My first reaction was it was disconcerting. It shows Rocky outside the ring, fighting the fight that he really can't win. It's a fight against the greatest opponent in the world; life. I said, 'No, kid, I think we're tampering with something here we should leave alone.' "

Stallone's agents and his wife Jennifer Flavin were desperate for him to make the movie - which stars Michael B. Jordan as 'Donnie' - to test himself on screen and depict Rocky in a way that audiences had never seen before.

And the 69-year-old action legend admired 29-year-old Coogler's commitment to the story and perseverance so much he decided to give him a chance to make his movie in the same way he was given an opportunity as a young man to make 'Rocky' in 1976.

In an interview with Deadline.com, Stallone revealed: "Coogler goes away and does 'Fruitvale Station', wins all these awards, and he's offered multiple job opportunities and he keeps coming back to 'Creed'.

"I see this and say, this fellow here obviously is functioning on a different kind of energy. It is heartfelt, not monetary, not ego. It's as though he has to finish a mission, which was a love letter to his father who had been very, very ill and that stimulated the idea.

"There was just something about this kid, who was very, very physical in his manner, but sensitive and emotional. It kind of reminded me...of me, truth be told. So I finally said, "You know what? Someone took a chance on me, once. I'm just going to throw caution to the wind and let him run with it."