CINCINNATI -- The Reds hoped to avoid surgery on the elbow of their top pitching prospect, Hunter Greene, but he and the club were left with no other choice. On Monday, it was revealed that Greene will need Tommy John surgery to repair the ulnar collateral ligament in his right elbow.

Reds medical director Dr. Tim Kremchek and Dodgers orthopedist Dr. Neal ElAttrache arrived at the diagnosis. ElAttrache will perform the surgery next week, keeping Greene out for the season. No immediate timetable was known for a return to the mound for the 19-year-old, who is ranked as the Reds’ No. 3 prospect and No. 36 overall by MLB Pipeline.

“He had a setback last week,” Reds president of baseball operations Dick Williams said during the late innings of Cincinnati's 4-3 loss to the Brewers at Great American Ball Park. “He threw to live hitters last Saturday. I was there and saw the session. It went well. When he was warming up several days later for another session of live BP, he felt some discomfort. We shut him down. We had the MRIs done, and there was new damage that occurred to the ligament.”

Greene first suffered a UCL strain while pitching for Class A Dayton on July 26. The prognosis at the time from the medical staff was that the injury wasn’t severe enough for surgery, and Greene and the club collectively opted to try rehabbing the ligament instead.

With hindsight, Williams and the Reds did not regret the decision of having Greene put off surgery.

“Obviously, there’s some lost time there,” Williams said. “We had some really good doctors look at him, that was their conclusion and he was cleared to throw back in the fall. He went through a program in the winter without setbacks. I think everybody was on board with what we did, and we wished that it worked. Now that it hasn’t, it was clear from the scans this time around that surgery would be required to make sure we get it repaired.”

Greene, the No. 2 overall selection in the 2017 MLB Draft, was 3-7 with a 4.48 ERA in 18 starts with Dayton last season. But his overpowering velocity made him an attractive prospect in high school and professionally. During the SiriusXM All-Star Futures Game in Washington last summer, all 19 pitches Greene threw were clocked at 100 mph or faster, with the phenom reaching a top velocity of 103.1 mph.

While Greene is not on the 40-man or 25-man Major League roster currently, he was expected to make a speedy ascent up Cincinnati’s system and be part of its future rotation when he was first drafted. Now that timetable is on hold for an extended period of time.