The rectus abdominis is a large muscle in the center of the abdomen that extends from the ribs to the front of the pubic bone. Matusz is the second player in the organization to undergo a form of sports hernia surgery, joining outfielder Lew Ford, who is now a free agent.
The 25-year-old left-hander is expected to be healthy for Spring Training.
"It didn't get worse; it actually stayed the same," Matusz said of the injury, which prevented him from sprinting but didn't bother him lifting or on the mound. "[I'm] doing rehab-type work right now. ... Within the next couple weeks, I plan on starting to lift heavy weights again. It's healing pretty quick."
After beginning the season as part of the Opening Day rotation, Matusz was moved to the bullpen in August and pitched to a 1.35 ERA in 18 relief outings, stranding all 14 runners he inherited. He allowed two earned runs on five hits and three walks over 13 1/3 innings pitched, striking out 19.
In five playoff appearances, Matusz pitched to a 1.93 ERA and allowed only two hits and one earned run -- Raul Ibanez's solo homer in Game 3 of the American League Division Series vs. the Yankees -- over 4 1/3 innings. He had five strikeouts and two walks (one intentional) over that stretch.
"It was something we were all aware of, but the trainers thought we could wait," manager Buck Showalter said Wednesday of the surgery, which Matusz had in Pennsylvania several days after the season ended. "He was pitching pretty good with whatever he had, so he will be fine."
Despite Matusz's dominance in relief, the team will take a look at him again as a starter this spring before determining his role for 2013.
Brittany Ghiroli is a reporter for MLB.com. Read her blog, Britt's Bird Watch, and follow her on Twitter @britt_ghiroli. This story was not subject to the approval of Major League Baseball or its clubs.