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07/17/09 10:03 PM ET

Astros place reliever Sampson on DL

Right-hander suffering from muscle spasms in shoulder

LOS ANGELES -- The Astros placed right-hander Chris Sampson on the disabled list prior to Friday's game against the Dodgers with muscle spasms in his right shoulder. The move is retroactive to July 10.

The club purchased the contract of right-hander Chad Paronto from Triple-A Round Rock. He is expected to be with the team in time for Saturday's game.

Sampson, who hasn't pitched since July 10, likely would not have been available for this weekend's series against the Dodgers after flying home Friday to be with this wife, Heather, who is expecting the couple's second child any day.

"You start to accumulate days, and even in the best-case scenario you begin to chew up the calendar," Houston general manager Ed Wade said. "Other than going short [on relievers] and having him rush back if Heather has the baby, if the knot is still in his neck, it just made sense to go ahead and do this."

Sampson is 4-1 with a 3.02 ERA and three saves in 47 2/3 innings covering 41 games this year. But he struggled in his last five outings before the All-Star break, allowing six earned runs in 4 2/3 innings (6.30 ERA).

Alberto Arias, who is 2-0 with a 1.52 ERA in 26 appearances, pitched in the seventh inning of a close game Thursday, a role which typically would have seen the Astros use Sampson.

"He's done a great job," manager Cecil Cooper said of Arias. "Every time he's gotten put in tough situations, he's been able to make pitches. He's done a good job."

Paronto is 2-1 with 15 saves and a 1.67 ERA in 27 relief appearances at Round Rock, throwing two scoreless innings Thursday. He went 0-1 with a 4.35 ERA in six games with the Astros last year, and is 6-12 with a 4.02 ERA in 171 career games with the Orioles, Indians, Braves and Astros.

Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.