Lohse has not pitched in the Majors since June 3, when he left a game against Cincinnati in the third inning with a strained right forearm. He is 4-4 with a 3.99 ERA in 10 starts.
St. Louis optioned right-hander Blake Hawksworth to Triple-A Memphis to make room on the roster for Lohse. Hawksworth pitched two scoreless innings in relief Saturday and has an ERA of 3.00 in eight appearances this season.
With lefty Dennys Reyes visiting an ill relative in Mexico, the move left the Cardinals with six relievers for the doubleheader. However, manager Tony LaRussa said starter Todd Wellemeyer would be available in relief.
Wellemeyer last pitched Wednesday in a loss to Milwaukee. Although he has pitched exclusively in a starting role the past two seasons, Wellemeyer has made 124 relief appearances in his career.
Andrew Simon is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.