Diaz, the Bucs' No. 8 prospect according to MLBPipeline.com, has been sidelined since March 16 due to right elbow soreness. Diaz was throwing as recently as last week, and Pittsburgh hoped the catcher would resume throwing to bases shortly afterward.
Instead, the unspecified surgery will further halt Diaz's ascent to the Majors. Head athletic trainer Todd Tomczyk has said Diaz's pain is on the outside of his right elbow, and the club doesn't believe it is related to his ulnar collateral ligament, which would seemingly rule out the possibility of Tommy John surgery.
"We'll know more after the surgery," manager Clint Hurdle said. "Obviously, his career's on pause right now. I think they're very optimistic about the surgery.
The 25-year-old was the Pirates' clear third option behind Francisco Cervelli and Chris Stewart. In his absence, Ed Easley and Jacob Stallings are the Bucs' Triple-A catchers.
Regarded as one of the Minor Leagues' best defensive catchers, Diaz hit .271/.330/.382 with four home runs and 47 RBIs in Triple-A last season.
"We wish him well. He's a well-thought-of young man," Hurdle said. "We like the player. We like the guy. We'll trust the doctors that they'll do a really good job."
Awards on the farm
Right-hander Tyler Glasnow, the Pirates' top prospect, was named the International League Pitcher of the Week on Monday. Glasnow threw 11 scoreless innings and struck out 18 batters while winning each of his two starts in Triple-A last week.
In five starts this season, Glasnow is 2-1 with a 2.08 ERA, 37 strikeouts and 12 walks in 26 innings. The 22-year-old righty is part of a dynamic Indianapolis rotation that has allowed one run over its past 35 innings.
Adam Berry has covered the Pirates for MLB.com since 2015. Follow him on Twitter at @adamdberry. This story was not subject to the approval of Major League Baseball or its clubs.