Until, that is, director Peter Segal approached them and asked them to play former fighters who go the distance one last time in the boxing comedy, "Grudge Match."
"I had no intention of doing this. I have no credibility in suggesting this. This came from all the other gentleman up here [on this panel.] Billy Gerber, Pete Segal and Michael Ewing. It was something I thought was absurd. I was like: 'Yeah, no. No one wants to see another boxing film, especially when you're approaching 160 years old and you're a little rickety and have bones coming out,'" Stallone, 66, said at a weekend press conference in New York.
"But then Robert called me and we talked a lot about it and the studio convinced me that I was completely wrong," Stallone laughed.
"I liked the idea of us doing it, so that was it. We never talked about [doing something like this] before," added De Niro, 70, who previously co-starred with Stallone in the 1997 drama, "Cop Land."
"It came from Pete. I met him at a party or something and he said, 'Are you interested in this thing?' And then it started. And then Billy Gerber [got involved] and so on and then Sylvester and I started talking," De Niro recalled.
"What attracted these guys to it was, obviously, we are winking at their iconography and so I'm always attracted to stories that straddle comedy and drama and I knew that this was, obviously, going to be a funny movie, but I also knew the fight had to be taken seriously for it to work and there were really only two people who could do that -- these two guys. The good and the bad of getting this green-lit -- the good was we knew who had to be in this movie, the bad was if we didn't get those guys, there would be no movie," Segal said. "Bob has had a little more experience lately, winking at 'The Godfather' with 'Analyze This,' so I had to convince Sly this was a way to do a really interesting story without holding a gun and killing someone."
Asked if there was any rivalry on the "Grudge Match" set, Stallone quipped: "I couldn't wait to fight him. I've been dying since 'Raging Bull.' I said: 'This is it; He's crossed a line.'"
"I remember the first day that Sly and Bob were in a scene together," producer Michael Ewing told the reporters at the press conference. "I remember after the first take, turning to Pete and going, 'Dude, you're directing De Niro and Stallone in this shot!' And he was like, 'I know!' And we were like teenagers. It was just really exciting."
"When you first realize you're going to be working with these guys and you're whole life of movies that you grew up with is suddenly standing in front of you and you're going, 'Holy [expletive,] what have we done here?'" Segal said. "And you look at Sly and Bob and then Alan [Arkin] joins the group and Kim [Basinger] and Kevin Hart, it turned it into a dream come true. And we all worked really hard getting the script ready and, that we were able to get this cast was extraordinary, and then to watch them work and the workouts these guys put in. Bob lost 35 pounds and Sly was in incredible shape. The amount of belief in the movie is tremendous and they all had it and that's why we were thrilled with how it came out."
So, have Stallone and De Niro seen each other's respective boxing movies "Rocky" and "Raging Bull," and, if so, what did they think of the classic boxing films?
"I never saw his movie. Was it any good? At first, I thought it was about homesteading," Stallone teased his co-star, who was sitting beside him on the panel. Getting more serious, he said: "It's probably one of the most brilliant biographies of all time. It's just incredible. It's timeless. What else can you say? It's just a perfect, perfect performance. Now I know he's not going to say that about me, so let's just move on."
"They are two different styles of film," De Niro said, comparing "Raging Bull" and the "Rocky" franchise, which includes six films to date.
"I was very impressed with the ones I saw, with what Sylvester had done with it as a craft, in all seriousness," De Niro said.
"Grudge Match" opens nationwide Dec. 25. It is rated PG-13.