Oakland Athletics right-hander Grant Balfour was placed on the 15-day disabled list with a strained right oblique.
The A's announced the move on Tuesday, retroactive to June 22.
Trystan Magnuson was called up from Triple-A Sacramento to take Balfour's roster spot. It is his second appearance in the majors this year.
Balfour is 4-1 with two saves and a 2.48 ERA on the season. He had allowed one run over his last 10 innings.
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