Source: Surgery for Daisuke Matsuzaka

BOSTON -- Red Sox pitcher Daisuke Matsuzaka has elected to have Tommy John ligament replacement surgery on his right elbow and intends to inform the team of his decision when he meets with club officials Thursday, according to a baseball source.

The surgery is expected to sideline the Japanese right-hander for at least a year, the usual recovery time for the procedure.

Matsuzaka, who has been on the disabled list since May 18, made the decision, the source said, after going home to Japan to discuss his options with family members, then meeting in Los Angeles on Tuesday with Dr. Lewis Yocum, who confirmed the Red Sox's diagnosis of a torn ulnar collateral ligament in the elbow. Nikkan Sports, a Japanese news agency, was the first to report Matsuzaka's decision.

Yocum, as did the Red Sox, told Matsuzaka that he had the option of rest and rehabilitation, the source said, but that if his elbow did not respond, he would have lost time that he could have devoted to recovering from surgery. The Red Sox had held out hope that the nonsurgical route might work, but never ruled out that surgery might be an option, saying further evaluation was required.

Matsuzaka decided that surgery was the best option, and intended to tell Red Sox GM Theo Epstein and Red Sox medical director Thomas Gill, who has been in communication with Yocum, of his decision.

The ulnar collateral ligament is one of the connective tissues that connects the humerus bone in the upper arm to the two bones of the forearm. It acts as a stabilizer in the elbow, allowing it to withstand the stresses created by throwing a baseball. When the UCL weakens and stretches, that is technically called a sprain, and prevents a pitcher from throwing with full velocity and typical control. A more complete tear requires the building of a new ligament, which Tommy John surgery accomplishes by transferring a tendon, often from the forearm.

Matsuzaka's place in the rotation has been taken by Tim Wakefield. John Lackey, who also had been on the disabled list with a strained elbow, pitched a minor league rehab start Tuesday, pronounced himself ready and is scheduled to start Sunday, in a slot that had been taken by Alfredo Aceves in his absence.

The Red Sox also recently signed veteran Kevin Millwood to a minor league deal after he opted out of a similar arrangement with the New York Yankees. Millwood made his first start for Pawtucket on Wednesday night and gave up four runs on five hits and two walks in just 2 2/3 innings.

Matsuzaka said he first experienced discomfort on April 29 in a start against the Seattle Mariners, a game in which he was pulled in the fifth inning because of what Francona called a stiff elbow after the game.

"But that was not a big enough deal to stop pitching," Matsuzaka said through translator Kenta Yamada.

Matsuzaka's turn was skipped after he came out of the bullpen on May 4 and pitched an inning of relief, taking the loss in a 13-inning, 5-3 defeat to the Los Angeles Angels. Four days later, he went six innings and was credited with the win in a 9-5 victory over the Minnesota Twins, but in his next start on May 16 he was dreadful, walking seven and giving up five hits in just 4 1/3 innings against the Baltimore Orioles.

Matsuzaka acknowledged that his velocity was down and that he was in pain. Data from the May 16 start (via BrooksBaseball.net) show that his fastball averaged just under 88 mph, and he topped out at 89. That's down 3-4 mph from what he has typically pitched.

"I couldn't throw as fast as before, but within this condition I tried to modify it,'' Matsuzaka said, according to Yamada's translation. "I was fortunate enough to win against Minnesota, but if I continue this pitching then I wouldn't help the team.

"In general, I could hold the pain and still throw before. But at this point, it's difficult to hold it with this kind of pain. So, I usually have a high tolerance, but this time it's hard for me to keep throwing."

Matsuzaka initially had said he was not concerned that he would need surgery, although at the same time he acknowledged his condition "was worse than I expected."

In each of the past two seasons, Matsuzaka had landed on the DL twice. Last year, he made only 25 starts because of a neck strain and a strained right forearm.

In 2009, he made just 12 starts and pitched only 59 1/3 innings. He was sidelined with a strained shoulder early in the season and again with the same injury that June.

In 2008, Matsuzaka set a career-high with 18 wins despite missing some time with a strained rotator cuff.

Matsuzaka, for whom Boston paid $103 million ($51 million posting fee, plus $52 million contract) to acquire from Japan before the 2007 season, is in the fifth year of a six-year contract. Assuming he is able to follow the normal course for recovery, it is conceivable that he will return in the second half of the 2012 season.

Gordon Edes covers the Red Sox for ESPNBoston.com.