Robert Downey Jr. says he was worried playing "Iron Man" for so long was going to affect his acting skills.

In a conversation with New York Times Magazine, Downey Jr. said the 11 years he spent playing Iron Man/Tony Stark in the Marvel Cinematic Universe began to make him wonder if he was cutting off other acting abilities he could be using.

"You start to wonder if a muscle you have hasn't atrophied," he said.

Downey Jr. took on the role for the first time in "Iron Man" in 2008 and performed as the character through 2019's "Avengers: Endgame."

He said that director Christopher Nolan, who cast Downey Jr. in "Oppenheimer," wanted to see a different side of him.

"I knew there was a point where Christopher Nolan was endorsing, let's work those other muscles, but let's do it while rendering you devoid of your usual go-to things," Downey Jr. explained.

In "Oppenheimer," Downey Jr. plays Atomic Energy Commission Chairman Lewis Strauss the movie about the invention of the atomic bomb, a project change in tone Downey Jr. said he welcomed.

"Coming from that other place, entering the box-office-weekend-dominating place, then going into this spot now where I'm happy that I'm in this quality product — I'm happy that I regained my connection with a more purist approach to making movies," he said.

"Oppenheimer" opens in theaters nationwide July 21.