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."

"Our condolences and prayers go out to Ryan's family as we grieve along with them over this tremendous loss."

Keeler, a highly touted, 6-foot-5 high school recruit out of Illinois, initially began his college football career with Rutgers ... but transferred to UNLV following his freshman season in 2022.

In his first year with the Rebels this past season, he played in two games ... recording a sack and eight total tackles.

One of Keeler's teammates last season, Adam Plant Jr., said he was "lost for words" after learning of the tragedy.

"Long Live Ryan Keeler gone way too soon," the former Rebels D-lineman said. "Love you forever brother."

Keeler was a pre-business major who had earned Academic All-Mountain West honors ... after recording a 3.80 GPA.

Rest in peace.