Last season's AL MVP sustained the injury when he grounded out in the fourth inning Friday night. He lunged at first base to beat the throw and came down hard on the bag. Mauer remained in the game, but the heel became more painful throughout the night.
"I'm pretty sore," said Mauer, who was listed as day to day. "It's probably a good thing I'm out. I'll rest it and get some ice.
"I really don't know what to expect," he added. "I've never had this. I'm hoping it doesn't last too long. Hopefully, it's just a couple of days."
The fact Mauer is a catcher could make the injury more complicated.
"It's something you don't want to mess around with," manager Ron Gardenhire said. "Heel bruises can really linger. We'll give him a day and see how he feels [Sunday]."
Mauer is fifth in the league with a .345 average. He batted .365 while winning his third batting title, and hit 28 homers with 96 RBIs last season. Mauer became the first catcher to win the AL MVP since Ivan Rodriguez in 1999.
The injury leaves the Twins with only one catcher. Drew Butera started Saturday night and batted eighth. Since the Twins don't know how long Mauer will be out, Wilson Ramos, the catcher at Triple-A Rochester, will join the team and could be activated in the next day or two.
The Twins are leading the AL Central despite not being able to keep their key players in the lineup. First baseman Justin Morneau returned Friday after leaving Tuesday's game with back stiffness. He hit a two-run homer in his first at-bat.