(Matt Slocum/Associated Press)

Nationals minor league left-hander Matt Purke will undergo Tommy John surgery Thursday morning to repair a torn UCL ligament, an operation that will sideline Purke, whom the Nationals signed to a $4 million big league contract out of the 2011 draft, for a year to 18 months. Dr. James Andrews will perform the procedure.

“It’s disappointing,” General Manager Mike Rizzo said. “He’s going to be a year-plus of getting back. But we’ve been through this before with good results, so we’re hoping for the same.”

Purke has suffered through injuries ever since the Nationals chose him in the third round out of TCU, battling through a series of shoulder ailments. He has made only 29 starts at Nationals minor league affiliates in his three-plus professional seasons. This season, Purke went 1-0 with an 8.04 ERA at Class AA Harrisburg, striking out 22 and walking 18 in 31 1/3 innings.

Because Purke signed a major league deal out of the draft, the Nationals have needed to keep him on their 40-man roster and option him to the minor leagues at the outset of each season. By the time Purke returns, he will be out of minor league options.

Purke will join Stephen Strasburg, Jordan Zimmermann, Sammy Solis, top prospect Lucas Giolito and several other Nationals pitchers who have undergone the elbow ligament-replacement surgery, which has become an “epidemic” in the sport. Purke had sought a second opinion last week for his sore elbow, and the Nationals found the results Wednesday morning.

While Purke received some of the worst news a pitcher can hear, the Nationals have no worries about Giolito, one of the top starting pitching prospects in baseball.

The hard-throwing right-hander has not pitched in a game for Class A Hagerstown since May 11, but that’s part of the Nationals’ plan, Rizzo reiterated. As Giolito finishes the final stages of his recovery from Tommy John surgery, the Nationals put Giolito on a throwing program so he can keep his arm fresh without racking up innings.

“He’s doing fine,” Rizzo said. “It’s part of his developmental program. He’s doing what pitchers do in between starts. He’s on an innings limit, but because of his young age, we want him to get through an entire season, to feel what it’s like to pitch at the end of a season.”

Of course, the Nationals’ plan for Giolito differs from how they treated Stephen Strasburg, whom they shut down in the middle of a playoff race. The critical difference: The Nationals believed that pulling Strasburg out of the rotation would have adversely affected his results. With Giolito in the minors, they prioritized his development over his results.