The 44-year-old Oscar-winning actor said he couldn't understand how he can be so bad, reported E! online.
"One of my first auditions was for one line in Star Trek, just one line in Star Trek: The New Generation. Great show, but I was terrible and I definitely did not get the part.
"I remember going up for WKRP in Cincinnati...They tried to remake the show. Definitely didn't get the part. I remember being so bad, just being so embarrassed reading. How can you be so bad?" Leto said.
"That's a little too naughty to talk about. I mean, that's a whole different show. It makes your head spin," he said.