"I'm definitely frustrated because I'm not out there doing what I love to do on an everyday basis," Harrison said. "I thought I could make adjustments to pitch through it, but it just wasn't working. The biggest thing is the weakness in my leg. ... The release point was inconsistent every pitch and I couldn't find a way to make it consistent, so I'm not doing myself any favors or the team any favors if I keep trying to pitch through it. So we might as well get it right."
Rangers President of Baseball Operations and General Manager Jon Daniels said the pitcher and club agreed it would be best to move forward quickly with surgery so he could potentially return for the stretch run.
Harrison could return sometime in mid-to-late July if his surgery and rehab go well. Dr. Andrew Dossett will perform the surgery Tuesday.
"Matt's particularly important to us and I think his decision to have it now rather than wait, once it seemed like this was where it was headed, we're all in agreement that it's the best thing for him and the club rather than wait and kind of waste two or three weeks," Daniels said. "It doesn't appear that rehab was going to be effective."
Since the start of 2011, Harrison has made more starts (64) and won more games (32) than any other Rangers pitcher. He was 18-11 with a 3.29 ERA in 32 starts last season and led the club with 213 1/3 innings pitched.
"It's a loss," manager Ron Washington said, "but we're not going to lay down because of it. We're going to fight just as hard and we're not going to make excuses."
Harrison's absence will further thin a pitching staff that continues to await reinforcements as injured pitchers Colby Lewis, Martin Perez, Joakim Soria, Kyle McClellan and Neftali Feliz undergo rehab.
Lewis underwent surgery last year to repair a torn flexor tendon. He will certainly return to the rotation when he's ready. He is currently expected to return in early June. Daniels said Lewis threw live batting practice Friday and is "every bit on schedule right now."
Perez is a candidate to rejoin the rotation upon his return from a fractured forearm sustained when he was hit by a line drive in Spring Training. Daniels said Perez would progress to throwing live batting practice in the next seven to 10 days.
Feliz, a starter last year until he was sidelined by an elbow injury that required surgery, is also expected to rejoin the team in the bullpen sometime in the second half of the season.
For now, the Rangers will stick with Nick Tepesch and Justin Grimm, who have a combined six Major League starts between them, in the fourth and fifth spots in the rotation.
Tepesch won the No. 5 job after a strong spring and is 1-1 with a 3.46 ERA in two starts this season. He has 10 strikeouts and three walks in 13 innings.
Grimm has made only one start this season after two spot-starts last year. He threw four innings in a no-decision last week in Seattle, allowing five hits and walking three. He will start again Sunday at home against the Mariners.
"I just want to show up and continue to get better," he said. "The only way to get better at this level is to get out there and compete against big league lineups."
For now, the Rangers must hope that Grimm and Tepesch keep improving -- or find someone else who can get the job done -- until reinforcements arrive.
"We've got confidence in the guys we've got out there," Daniels said. "We've got some guys in Triple-A that are throwing the ball well. This is the nature of the beast. You know going into the season you're going to have injuries, you're going to have issues, you just don't know exactly who it's going to be or when. ... The fact that there's a likelihood that we'll see Matt again in the second half, I'm sure we'll need him. That's reassuring. It could be worse."