Harrison, who hasn't pitched in two weeks, was placed on the 15-day disabled list because of an inflamed nerve in his back. He was hopeful treatment and two epidural injections would get him back on the mound.
They didn't work.
"Any time you have an injury, it's frustrating," Harrison said. "[The surgery] was the last resort to get it right. Hopefully, this works. I have to do what I have to do to get through it."
The Rangers will turn to rookie right-hander Justin Grimm. Grimm will make his fourth career start Sunday against the Seattle Mariners. He went four innings in his first start this season, allowing two runs on five hits April 11 at Seattle.
Another rookie, Nick Tepesch, is scheduled to make his third major league start Saturday. Tepesch was brilliant in his major league debut against the Tampa Bay Rays, allowing one run in 7 1/3 innings. He pitched into the sixth inning Sunday in Seattle, allowing four earned runs.
"That's where we have them now [in the rotation]," Rangers manager Ron Washington said. "It's important that they pitch well."
Harrison said he felt pain down to his foot after running recently. Before that, the pain and numbness had gone only down to his left knee.
He had his second injection last weekend. The Rangers were hopeful Harrison could work through a rehabilitation program to improve his back, but once the injection wore off, the numbness started going down his left foot, Harrison said Friday.
Harrison went to get a second opinion from Dr. Robert Watkins in Los Angeles, returning Thursday to see Rangers spine specialist Dr. Drew Dossett.
"The symptoms are not reacting or responding the way we hoped they would to the injections," Rangers general manager Jon Daniels. "We'll have a better idea on the timetable after the surgery."
Daniels said the percentages on this type of surgery are very good. Harrison is confident he can return this season. He's had surgery before for thoracic outlet syndrome in 2009, and has won 34 games the past two seasons.
"I know what I have to do to get back," Harrison said. "That's one thing I have on my side."
Harrison, an 18-game winner last season, signed a $55 million, five-year contract during the offseason. He was affected by the injury this season, going 0-2 with an 8.44 ERA as he tried to pitch through the soreness.
"Losing any of your guys, it's never good news," Daniels said. "Matt's particularly important to us. His decision to have it now rather than wait once it seemed like this was headed, we're all in agreement this is the best thing for the club."
The Rangers have reinforcements, but they aren't immediately available. Right-hander Colby Lewis, coming back from right flexor pronator surgery in July, has one or two live batting-practice sessions left before he will pitch in an extended spring training game.
"He's every bit on schedule," Daniels said. "We're not going to push him at all."
Potential starters Martin Perez, Neftali Feliz and Kyle McClellan also are on schedule in their rehab programs, but they're still not close to returning. Perez is coming back from a broken left wrist, and McClellan from a strained right lat muscle.
Feliz, who had Tommy John surgery in August, won't make it back until after the All-Star break.
"It's comforting to know we'll have Harrison back before the season is over," Washington said. "It's comforting to know that the young kids that we are putting in there are handling their business. But you would definitely rather have Harrison."