The 39-year-old has spent parts of 11 seasons in the Major Leagues while posting a career 4.93 ERA. He is expected to temporarily serve in long relief as the Blue Jays return to an eight-man bullpen while Brett Lawrie is on the disabled list with a strained left oblique muscle.
"We just figured if, God forbid, something happens, someone gets hit early and we need that length, knowing we have another two weeks without an off-day, better just to be safe to be protective that we don't tax the bullpen," Blue Jays general manager Alex Anthopoulos said.
"Ortiz will be able to insure us if we go to extra innings or something happens early in the game, he'll be able to go five or six."
Outfielder Casper Wells was designated for assignment to make room for Ortiz on the 40-man roster. Wells was claimed off waivers by the Blue Jays last week, but did not receive any playing time during his brief stint with the club.
The timing of the roster move seemed a little odd considering Jose Bautista was not in the starting lineup against the White Sox because of a sore back, leaving Toronto with a very short two-man bench for Monday's game.
With Bautista out of the lineup, Toronto opted to use catcher J.P. Arencibia in the No. 3 hole, while Mark DeRosa got the start at third base and Emilio Bonifacio started in right field.
Evan Peaslee is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.