The Royals announced that Lamb, one of the organization's top left-handed prospects, will have ulnar collateral ligament reconstruction, or "Tommy John" surgery, on his left elbow tomorrow. The surgery will be performed by Dr. Lewis Yocum in Los Angeles.

Lamb, 20, entered the season ranked by MLB.com as the No. 34 prospect in baseball. He has not pitched since May 19, when he left his start with elbow soreness after throwing eight pitches. The Royals placed him on Double-A Northwest Arkansas' disabled list the following day.

The Laguna Hills, Calif., native made eight starts for the Naturals in 2011, going 1-2 with a 3.09 ERA in 35 innings. He was 10-7 with a 2.38 ERA and 159 strikeouts in 147 2/3 innings last year for three teams en route to being named the 2010 Paul Splittorff Award winner as the organization's top pitcher.

He throws a fastball, curve and change and has generally been known for outstanding command. He'd gone six innings in each of his three previous starts before leaving early against Tulsa -- his best effort came May 14 when he held Springfield to one run on a pair of hits over six frames for his only win.

Lamb was selected by the Royals in the fifth round of the 2008 Draft out of Laguna Hills High School. The 6-foot-4 lefty attended his first Major League Spring Training with the Royals this spring, throwing one scoreless inning and striking out three in one relief appearance.