To make room on the 25-man roster, Toronto optioned right-handed reliever Chad Franklin to the International League farm team.
Kratz will serve as a backup to Josh Thole. Regular starter Dioner Navarro strained his right quadriceps Thursday and will be held out of the next few games. Navarro will not be placed on the disabled list according to manager John Gibbons.
''We just think it'll maybe be a couple days,'' Gibbons said. ''We had to cover ourselves with another catcher.''
In seven games with Toronto earlier this season, Kratz batted .200 (2 for 10) with a home run and four RBIs.