The move, retroactive to July 11, was revealed by Baltimore manager Buck Showalter after Saturday night's game against Cleveland and made official on Sunday.
Guerrero has not played since being struck in the hand by a pitch from Boston's Kyle Weiland on July 10. He's batting .279 with seven homers and 31 RBI.
Showalter hopes to have Guerrero back on July 26 against Toronto..
In other moves, the Orioles optioned left-hander Pedro Viola to Double-A Bowie and recalled outfielder Matt Angle and pitcher Troy Patton from Triple-A Norfolk. Angle, who hit .266 with the Tides, was to bat leadoff and play left field Sunday against the Indians.