Stephen Dorff only had “six or seven weeks” to get into believable shape as a UFC champ in “Embattled,” and somehow he did it.

“I was coming off ‘True Detective’,” he told The Post. “I would have liked to have had three months, but I had six or seven weeks and jumped right in with my physical trainer. Put as much size on me as possible.”

Dorff continued to explain his prep work for the film, which is now streaming on Amazon Prime: “[I] put on about nine pounds of muscle by eating and exhausting training and we had to kind of Cliff Notes it because we didn’t have the time.”

The actor noted that “you can’t over-train. You need the muscles to rest. It’s just a question of hitting it every day and eating a lot. The truth is I’m pretty lean most of the time. I was a little skinny at the end of ‘True Detective,’ I needed to build up my back and lats and shoulders and then you have muscle memory.”

Cliff Notes or not, the 47-year-old actor looks entirely believable as a seasoned fighter who goes up against his son.

“It’s a really dark look at father-son relationships against the backdrop of UFC which is bigger than it’s ever been,” he explained.

It’s nothing like the relationship he had with his father, songwriter Steve Dorff, who penned “Every Which Way But Loose,” the Eddie Rabbitt title track from the 1978 Clint Eastwood film.

Dorff said his parents were “incredibly nurturing” and credits them for not falling prey to the excesses that Hollywood offers young stars. After all, he started acting as a kid, appearing on sitcoms like “Roseanne,” “Married…with Children,” and “Blossom.”

He first gained widespread attention for 1992’s “The Power of One” opposite Morgan Freeman, Sir John Gielgud, and the next year starred opposite Alicia Silverstone in the music video “Cryin’” by Aerosmith. Since then, Dorff has balanced his career between big-budget movies like “World Trade Center” and more indie fare like John Waters’ “Cecil B. Demented.”

“I always looked up to the guys who were older than me, the Sean Penns, the Johnny Depps, and I looked at their careers and their choices and how they would make a big movie but then make a movie with John Waters or a tiny movie with Jim Jarmusch,” he said.

“I always thought that was interesting if you could have a career at the end of the day that’s not one specific thing,” he added. “ ‘Oh he’s been an action star for eight years and now he’s doing insurance commercials.’ I didn’t want to have that career. I wanted to work with great directors and have great experiences.”

Dorff said  part of what he loves about acting is the opportunity to learn about other disciplines like architecture and art.

The “Public Enemies” star reveals that through Dennis Hopper he has been able to meet artists like Ed Ruscha, Cy Twombly, and Kenny Scharf and has collected art over the years.

“I’ve sold some stuff along the years when I needed some extra moola,” he admitted. “I had so many opportunities that I could kill myself for not taking back in the day. But you live and you learn. I’m hoping I never have to sell again. And I’m not in that game of flipping them. I look at art as pictures I want to look at.”

“Embattled” is available to stream now on Amazon Prime, iTunes, Vudu, Google Play, and DirecTV.