Jerry Hairston Jr. is one of many in the baseball world mourning the passing of Fernando Valenzuela this week ... telling TMZ Sports his admiration for the Dodgers legend was endless.
Hairston Jr. actually had the chance to work with the former pitcher over the last few years of his life ... as the two both had gigs broadcasting L.A. games -- and he had nothing but great experiences with the guy.
He told us he actually went golfing a few times with Valenzuela ... and the two shared many laughs while out on the course as well as at Dodger Stadium.
"He was humble, he was kind and he was funny," Hairston Jr. said. "The banter that not only me and him shared, but the rest of our colleagues and the rest of our former players, his humor was second to none."
"We're going to miss Fernando," he added. "63 is far too young."
A cause of death for Valenzuela -- who won Rookie of the Year honors as well the Cy Young award while with the Dodgers in 1981 -- has not yet been revealed ... although Hairston Jr. said he and others close to the former ace knew he had been battling an illness in the final weeks of his life.
"He left a lasting legacy," Hairston Jr. said, "and Fernando will never be forgotten."
The Dodgers, meanwhile, will try to win the upcoming World Series for Fernando ... and Hairston Jr. told us he's expecting an epic showdown with the Yankees -- a matchup Valenzuela would have certainly loved.