The 49-year-old former defensive lineman did not reveal who within Las Vegas' org. made the claims ... but he did say he was surprised footage from the workout never got leaked.
"I'm wondering how the hell this happened," Sapp said, "and the tape didn't get out, right?"
As we reported, Kaepernick tried out for Vegas in late May ... but the Raiders have been tight-lipped about the workout ever since, with head coach Josh McDaniels declining to get into specifics of how it all went.
Kaepernick's agent, Jeff Nalley, denied Sapp's claims in a text message to Pro Football Talk on Sunday .