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07/23/08 8:05 PM ET

Prospect Rasmus sprains knee ligament

Cards Minor League outfielder will miss at least a month

ST. LOUIS -- Already riddled by injuries at the big league level, the list of hampered Cardinals took another hit on Wednesday.

Colby Rasmus, widely considered as the top Minor League prospect in the organization, discovered he has a Grade I medial collateral ligament sprain in his left knee after undergoing an MRI on Wednesday. Rasmus damaged the knee in the bottom of the first inning while playing center field Tuesday night.

Rasmus will miss at least a month with the injury, and he has withdrawn from the U.S. team for the upcoming Olympic Games in Beijing.

Rasmus got off to a slow start for Triple-A Memphis, but has recently improved his batting average to .249 with a .346 on-base percentage. He has belted 11 home runs and has driven in 36 runs.

According to The Associated Press, outfielder Nate Schierholtz, a San Francisco Giants prospect, of Triple-A Fresno, will replace Rasmus on the Olympic roster.

Lee Hurwitz is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.