"The Rangers will be without All-Star third baseman Adrian Beltre until the end of August after he aggravated a strained left hamstring Saturday.

Beltre pulled up lame about halfway through an afternoon running session on the basepaths. An examination determined that he had aggravated the original injury. Club physician Keith Meister said Beltre will be out about another three weeks.

Beltre went on the disabled list July 22. The club had hoped he could return during the 10-game trip that begins Friday at Oakland, but the latest development dashed the plan.

"Hamstrings are fickle," manager Ron Washington said, with a sigh in his voice.

The setback came after the Rangers' medical staff changed its plan for Beltre's treatment. He ran Friday and was scheduled for a day off before a second session Sunday. According to Washington, that plan was changed to "two or three days in a row" before a break."