Santos was expected to arrive in Toronto before Saturday's contest, but he will receive another day off before being activated.
"He was unable to play catch because it rained out there in [California] the last two days, and he's probably working on limited sleep," Blue Jays manager John Farrell said. "We don't feel like we are going to rush him into today's action. He'll be available tomorrow."
Farrell wants Santos actively throwing the ball before he gets him back into a game, as he hasn't thrown since collecting his first save of the season Wednesday against Boston.
Santos is on a throwing program that calls for him to toss every day, so Farrell wants to be careful with his closer.
"[It's] somewhat precautionary, but I think it's the prudent thing to do in Sergio's case," Farrell said.
Farrell said a decision on Evan Crawford, who was recalled from Double-A New Hampshire in the absence of Santos, is still to be determined. To make room for Santos on the 25-man roster, the Blue Jays will have to make a roster decision before he is activated.
Santos has missed the past two games as he went to California to be with his wife, who gave birth to the couple's third child, a boy, on Thursday.
The 28-year-old has appeared in four games this season and has converted one of three save opportunities.