The AL East leaders also optioned infielder Nick Franklin to Triple-A Durham on Thursday.
In parts of three seasons with the Angels and Houston Astros, Krauss has batted .194 with 11 homers and 39 RBIs. The left-handed hitter has spent most of this season with Triple-A Salt Lake, batting .289 with four homers and 29 RBIs.
Franklin has appeared in 28 games this season, batting .139 with one homer and three RBIs while learning to play first base, where the Rays need help because of injuries.
Rays vice president of baseball operations Erik Neander calls Krauss a disciplined hitter who will add left-handed power to the roster.