The cause of death of John Elway‘s longtime agent and friend Jeff Sperbeck has been officially ruled as blunt head trauma, TMZ Sports has learned.

The Riverside County Sheriff’s Office told us Friday the Coroner’s Bureau made the determination just days after Sperbeck’s April 30 passing … adding the death has also been ruled an accident.

A final report in the case is expected to be released once toxicology results return.

As you know, Sperbeck was catastrophically injured back on April 26 — when he fell off a cart Elway was driving inside of a swanky golf community in La Quinta, Calif.

Police have been investigating the incident — though Sheriff Chad Bianco said on May 2 they had found no reasons to believe any criminal activity occurred.

Elway mourned Sperbeck’s death publicly in the hours after his passing … writing in a statement, “There are no words to truly express the profound sadness I feel with the sudden loss of someone who has meant so much to me.”

Sperbeck’s family added that Jeff “was a wonderful father, husband, brother, son and friend to many” who “will be profoundly missed by all.”

Sperbeck was just 62 years old.