Matthias Schoenaerts with co-star Marion Cotillard in a scene from 'Rust and Bone.' Associated Press

The French actress Marion Cotillard is getting most of the media attention for her fearless performance as a former whale trainer who, after a freak accident, loses her legs in "Rust and Bone," which Sony Pictures Classics released on Friday.

But her co-star, the 34-year-old Belgian actor Matthias Schoenaerts, is her equal, giving an emotionally grounded performance as her unlikely lover: an amateur boxer, a club bouncer and a man struggling with single fatherhood. The only thing standing in Mr. Schoenaerts's way when it comes to Hollywood stardom might be that there are two many vowels in his last name.

Not that Mr. Schoenaerts is much interested in fame, he said, over a steak lunch at an uptown hotel where he was promoting the movie earlier this month—something he has been doing since it premiered at Cannes in May. (He and Ms. Cotillard are also expected at a lunch for the movie Tuesday at Brasserie Ruhlmann, the day after Ms. Cotillard receives a career tribute at the Gotham Independent Film Awards Monday night.)

The journey to being an American movie star, Mr. Schoenaerts said, can often feel like being in the spin cycle of a Laundromat and "it never ends."

Mr. Schoenaerts earlier this month. Adriel Reboh/Patrick McMullan

He also compared Hollywood to a supermarket—"we can throw him away as fast as we took him," he said—and doesn't want to know if his agents or studio executives imagine him as the next Garrett Hedlund, the next Michael Fassbender or the next Clive Owen.

"I don't want to look at myself that way," he said, polishing off his steak in record time. "I don't understand that. It doesn't make sense. It's a weird way of thinking about yourself."

He prefers spending time in New York and keeping a full-time residence in Antwerp. "I like Belgium and I like to have this hideout, to be able to have this place to retreat and to step back and look at it from a distance," Mr. Schoenaerts said. There are tabloid magazines there, but no real paparazzi or as he described it, a star culture. "We don't have Justin Bieber kind of problems," he said.

The cinema in Belgium is split between French language art-house filmmakers like the Dardenne brothers and a more mainstream Flemish speaking side. From the Flemish segment, "there's a generation of filmmakers making personal films that appeal to a greater audience."

Mr. Schoenaerts—who has been acting since he appearing in a stage production of "The Little Prince" opposite his late father, the actor Julien Schoenaerts—broke out in one of those crossover films, "Bullhead," which was nominated for an Academy Award for Best Foreign Film earlier this year.

It was through "Bullhead" that "Rust and Bone" filmmaker Jacques Audiard, who most recently made "The Prophet," came upon Mr. Schoenaerts. "I don't know if he's crazy," said Mr. Schoenaerts of Mr. Audiard. "Maybe all the other ones are crazy for not being like him. He wants to film truth, he doesn't want to film acting. Acting for him isn't about tricks and vanity; it's about being simple and authentic and sincere. He's the first true actor's director I've ever worked with."

Through CGI, Ms. Cotillard's legs are erased for the finished film. Meanwhile, Mr. Schoenaerts had to both work out heavily and gain weight for his role. Mr. Audiard "wanted the character to look strong but not fit," said Mr. Schoenaerts. "He's hit rock bottom before the film starts. He's been eating out of garbage cans. The guy looks unhealthy but you see he's strong. Maybe somewhere in the past he could have been an athlete."

So, he hit the gym to gain weight and then "ate a lot of crap: ice cream, pizza, just nasty stuff." Because he was boxing to train and that burns a lot of carbs, "I had to eat twice as much junk. If I look at it in retrospect, I think, Wow that was crazy. But when I was doing it, it didn't seem crazy at all."

Crossing over to American cinema, Mr. Schoenaerts is concerned about falling into the cliché of the European villain, though he wouldn't turn down playing James Bond if and when Daniel Craig decides to hang up his suit. "I like to play underdogs and antiheroes," he said. "I don't like to play classical heroes."

He recently shot an art-house crime thriller in New York with Mr. Owen and Mila Kunis called "Blood Ties," directed by Ms. Cotillard's partner, Guillaume Canet, as well as an English-language remake of his Flemish hit "The Loft." He's rumored to star opposite Michelle Williams in a film version of the Irène Némirovsky novel "Suite Francaise."

"I'm hoping for exciting experiences. I just want to do stuff that I feel and I like because then I'm at my best. There are a lot of great filmmakers here," Mr. Schoenaerts said, looking for a cigarette. "I'm not in a hurry I'm not in a rush, I don't have this crazy need or ambition."

Write to Marshall Heyman at