LAS VEGAS -- Merkin Valdez's lingering physical woes prompted the Giants to select right-hander Luis Perdomo in Thursday's Rule 5 Draft at the Winter Meetings.

Valdez, 27, felt continual tightness in his forearm while pitching for Escogido in the Dominican Winter League and is scheduled to undergo open surgery Monday in San Francisco. The right-hander, whose rehabilitation is expected to last six to eight weeks, should be "on the mound and somewhat competitive when Spring Training starts," head athletic trainer Dave Groeschner said.

Valdez underwent Tommy John elbow surgery in September 2006 and missed most of last season with a strained right elbow. He emerged healthy after pitching for the Giants' instructional league club in late September and early October, but made only three Winter League appearances before he was ordered to return to San Francisco for tests and examinations by club doctors. Valdez also received a second opinion from noted orthopedist Lewis Yocum.

The possibility that Valdez could remain sidelined made Perdomo an attractive choice for the Giants.

"It's a no-lose situation," said Giants general manager Brian Sabean, referring to the nature of the Rule 5 Draft. If Perdomo doesn't stay on the Giants' Major League roster all season, he must be offered back to St. Louis, his previous organization, for $25,000, which is half of the Rule 5 Major League selection price. Frequently, teams engineer low-level trades to allow them to keep drafted players.

Perdomo, 24, finished 7-3 with a 2.36 ERA and 20 saves for three Minor League teams last season: Cleveland's Class A Kinston affiliate and Double-A Akron club and St. Louis' Springfield outpost. He struck out 82 and walked 30 in 72 1/3 innings while limiting opponents to a .190 batting average. The Cardinals obtained Perdomo and cash for right-hander Anthony Reyes in late July.

Giants vice president of player personnel Dick Tidrow said that Perdomo possesses two above-average pitches -- a fastball that ranges between 93-95 mph and a slider. Perdomo's currently trying to refine his changeup while pitching for Aguilas in the Dominican Winter League, where he's 0-1 with a 14.54 ERA in seven appearances.

"His stats aren't good, but the reports are," Tidrow said.

The Giants also lost outfielder Ben Copeland to the Oakland A's later in the Draft's Major League phase. Copeland had the distinction of being San Francisco's top pick in the 2005 First-Year Player Draft despite being selected in the fourth round. The Giants forfeited their earlier choices by signing multiple Major League free agents the previous year.

Copeland, 24, ascended through the Giants' system last season. He hit .261 with an Eastern League-high 13 triples for Connecticut, then batted .341 in 22 games with Triple-A Fresno.

Tidrow said that Giants weren't too surprised to lose Copeland.

"We've been doing a good job drafting, and when you do that, you just can't protect everybody," Tidrow said.