Santos was placed on the DL on May 12 with a strained right elbow. He made two rehabilitation appearances for Double-A New Hampshire, allowing four runs in two innings.
Santos provides manager John Gibbons an option for Brett Cecil, who left Friday night's game against Baltimore with groin tightness and will likely be rested for a few days.
Before the injury, Santos was 0-2 with a 9.00 ERA and five saves in 14 appearances.
To clear a roster space for Santos, the Blue Jays on Saturday optioned outfielder Darin Mastroianni to Triple-A Buffalo.
Mastroianni, who was recalled from Buffalo on Thursday, is 0 for 13 this season with Minnesota and Toronto.