Paul Rudd threw his towel before his on-screen nemesis Kang The Conqueror, played by Jonathan Majors, bulk-up physique.
Appearing on The Graham Norton show, the Ant-Man star said it was "pointless" to copy the shape of his co-star.
"He was terrifying, and it was pretty intense," Rudd continued. "I tried to bulk up and get in shape, but it was pointless compared to Jon, and why do it when Ant-Man never takes his shirt off!"
Previously, speaking to Men's Health, the 53-year-old said that he "worked really hard" to get in Ant-Man shape for the third part of the franchise, adding it was "so much harder" than compared to the first and second films in 2015 and the 2018 sequel Ant-Man and the Wasp, respectively.
"I had fallen off more than I had in the past," he said. "All of a sudden, my clothes fit tight. And I thought, 'God, this sucks. I can't even wear these pants.'"
"So I'd say to myself, 'Well, I might as well just eat some of these cookies.' I was irritable and self-conscious. I just wasn't in a good mood. I really beat myself up," the actor added.