LAS VEGAS — San Francisco Giants right-handed reliever Merkin Valdez is scheduled for surgery on his throwing forearm Monday, another setback for one of the club's top prospects who underwent reconstructive elbow surgery in the fall of 2006.

Valdez, who was sidelined most of the 2008 season with elbow and arm trouble, had been throwing in his native Dominican Republic but was shut down because of constant tightness in his arm. He traveled to San Francisco to be evaluated by team doctors, then received a second opinion from Dr. Lewis Yocum.

The procedure Monday will involve cutting a band of tissue in his forearm to release the pressure and discomfort he's experiencing, San Francisco athletic trainer Dave Groeschner said. The timetable for returning to the mound to begin a throwing program is 6-to-8 weeks.

"Merkin's iffy," Giants general manager Brian Sabean said Thursday, the final day of the winter meetings.

San Francisco on Thursday selected right-hander Luis Perdomo with the sixth pick in the Rule 5 draft from the St. Louis Cardinals' Triple-A Memphis affiliate — giving the Giants another option and some insurance in the bullpen. Players chosen in the Rule 5 draft must stay on the active major league roster with their new club all season or be offered back to their old team for $25,000.

The hard-throwing Valdez, 27, was placed on the disabled list in May with a strained elbow on his throwing arm, though the inflammation and tightness wasn't believed to be related to his surgery on Sept. 27, 2006.

"That looks great," Groeschner said of the elbow.

After missing all of the 2007 season following his Tommy John surgery, Valdez made the opening-day roster this season for the first time. Many other clubs expressed interest in acquiring him during spring training, too, but Sabean wasn't about to let him get away.

Valdez went 1-0 with a 1.69 ERA in 17 appearances and 16 innings, including one start, in 2008. He had limited opponents to a .222 average over his final 16 outings with 12 strikeouts and six walks for a 1.20 ERA during that span.

"We tried to explore every other treatment option, but we pretty much ran out," Groeschner said.