A featured lightweight bout between Gilbert Melendez and Rodrigo Damm has been upgraded to an interim championship title match at Strikeforce “Shamrock vs. Diaz” this Saturday at the HP Pavilion in San Jose, Calif.

Melendez, who turns 27 on Sunday, was originally slated to face Strikeforce lightweight champion Josh Thomson (16-2) in a rematch of their June 2008 showdown. However, Thomson broke his leg sparring on April 1 and was forced to withdraw.

The 30-year-old San Jose native underwent surgery for the injury Wednesday and told Sherdog.com via text that “everything went well.” Thomson, who had a plate and eight screws inserted in his left leg, did not have an immediate timetable for his recovery time and return.

A star on Japan’s competitive lightweight circuit, Melendez (14-2) hasn’t stepped back into the cage since his five-round shutout loss to Thomson. The mop-topped 26-year-old wrestler holds key victories over standouts Clay Guida and Tatsuya Kawajiri, and a close decision loss to top-20 ranked Mitsuhiro Ishida at Yarennoka’s 2007 New Year’s Eve event.

Damm (8-2) was introduced to the U.S. audience through his appearances on the Ion Network’s “Bodog Fight” TV series, where the Alliance Jiu-Jitsu rep submitted K-1 regular Kultar Gill and current TUF 9 competitor Santino Defranco. The lanky Brazilian stopped American Top Team standout Jorge Masvidal with second-round strikes at Sengoku “Third Battle” last June, but was submitted by Eiji Mitsuoka at their next event last August.

In Strikeforce’s main event, former UFC middleweight champion Frank Shamrock will take on the equally outspoken Nick Diaz at a 179-pound catch-weight. Bangers Benji Radach and Scott Smith will also duke it out in a featured middleweight bout.

Strikeforce “Shamrock vs. Diaz” will air live on Showtime at 10 p.m. EST. The event will also be streamed live with interactive extras at http://strikeforce.sho.com for $24.95.