DENVER -- A recurrence of discomfort in right-hander Merkin Valdez's strained throwing elbow has interrupted his injury rehabilitation stint and will force him to undergo an MRI on Wednesday in the Bay Area.

Giants head athletic trainer Dave Groeschner said Tuesday that Valdez's arm felt "dead" while playing catch Sunday, one day after pitching a scoreless inning for Class A San Jose. Valdez, who was scheduled to pitch for Triple-A Fresno against Colorado Springs on Monday, instead was examined by Dr. Ken Akizuki, the Giants' team orthopedist.

Groeschner reiterated that Valdez's injury does not stem from the Tommy John elbow surgery he underwent on Sept. 27, 2006. Groeschner added that Wednesday's test should result in a more conclusive diagnosis on Valdez. The 26-year-old had thrived in 17 appearances, posting a 1-0 record and a 1.69 ERA while stranding 11 of 12 baserunners.

Unlike Valdez, right-hander Kevin Correia did pitch for Fresno on Monday and remained on course to start Sunday against Oakland by allowing one run and five hits in seven innings as the Grizzlies prevailed, 3-2.

In other pregame developments, manager Bruce Bochy tweaked the lineup by starting rookie Travis Denker for Ray Durham at second base and right-handed-batting Rich Aurilia at first base instead of John Bowker, a left-handed hitter, against Rockies right-hander Aaron Cook.

Although Durham entered the game with a career .351 average (13-for-37) against Cook, Bochy explained that the 36-year-old needed a break after starting all four games at steamy Washington in the Giants' previous series. Regarding Aurilia, Bochy indicated that wanted to keep the veteran's stroke sharp, especially since Bowker started each game at Washington and wouldn't be prone to becoming rusty.