"You're always hopeful that rehab is going to work," Brewers assistant general manager Gord Ash said, "but in this case, it didn't."
Williams underwent a platelet-rich plasma injection earlier this season in an effort to avoid surgery. The same therapy proved successful for another right-hander, Tyler Thornburg, who missed most of last season with an elbow injury but avoided surgery and is currently in the Major Leagues.
A power pitcher drafted by Milwaukee in the fourth round in 2013, Williams may have done too much, too soon to impress in his first big league Spring Training camp. He drew comparisons to All-Star closer Craig Kimbrel after Brewers hitters stood in the batter's box against Williams in February, with Ryan Braun praising "as good a fastball as I have ever seen in live BP."
Now Williams faces a year-long rehabilitation. The hope, Ash said, is that he will be ready to return to the mound next August before making up for lost time in the fall instructional league. Williams just turned 24 last month.
In other Brewers news on Saturday:
• Infielder Hector Gomez, designated for assignment on Friday, declined an outright assignment to Triple-A Colorado Springs and became a free agent.
• There was plenty of birthday cake to go around before the Brewers faced the Cardinals on Saturday night. Brewers GM Doug Melvin, amateur scouting director Ray Montgomery, third-base coach Ed Sedar and senior administrator Barb Stark celebrated birthdays. Melvin turned 63, Montgomery 46 and Sedar 54.
Stark was one of then-Brewers owner Allan H. "Bud" Selig's first hires after he bought the franchise and moved it to Milwaukee in 1970.
Adam McCalvy is a reporter for MLB.com. Follow him on Twitter @AdamMcCalvy, like him on Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.