"I love him but those look airbrushed," one baffled user wrote.
"It looks fake," another declared.
"Are they even real?" one person mused.
One said: "This doesn't look real."
Other suggested his tanned torso had been enhanced with makeup, saying he'd "contoured" his six-pack before appearing on the show.
While the Baywatch star hasn't officially commented on his super jacked physique, the fact he works out is no secret.
The 31-year-old regularly posts videos of his gruelling workouts at the gym with his 38.8 million followers.
Many show the former High School Musical star completing insane physical achievements, such as the time he challenged The Rock — who is also a very fit and athletic human — to a tyre flipping contest. There was also the time he confronted a terrifying rope climb and the time he carried a really heavy piece of equipment on his shoulders.
During the interview — in which he came face-to-face with the latest waxwork figure of him, modelled on his Baywatch character — he commented on how "unrealistic" his own body is.
"For guys that's (points to his body) unrealistic...I got very big and buff for that movie but I don't want people to think that's the best way to be," he said. "Be your size. I don't want to glamorize this."
Back in 2016, Efron revealed in a tweet exactly how he got so shredded, and it was intense.
