UNLV defensive lineman Ryan Keeler has tragically died ... the school announced the redshirt freshman football player passed away on Monday.
He was just 20 years old.
Keeler died in Las Vegas, according to the university ... but no other details surrounding his death have been revealed.
School officials mourned his passing late Monday night, with the team's new head coach, Barry Odom, saying they're all "devastated to have lost a member of our Rebel family."
"While I had the honor of knowing Ryan for only a couple of months," said Odom, who was hired in December, "he already stood out to our coaching staff as an incredible person, student and teammate.