Denver Nuggets star Jamal Murray claims he's been HACKED ... and a graphic video that surfaced on Instagram on Saturday was never intended for public consumption.
The video in question popped up on the 23-year-old's IG stories late Saturday night and was deleted a very short time after it went up -- but it still left his 450k followers in shock.
Sunday morning, addressed the situation head-on ... saying "First and foremost I would like to apologize to my fans. My account has been hacked, currently working on the issue. Thanks."
Obviously, we're not gonna post the video here.