Manager Paul Molitor made the announcement after Thursday’s 3-1 loss to the Tigers, one in which Sano was not in the lineup.
Molitor told reporters he wasn’t unhappy with Sano’s effort, but believed the move would help the 25-year-old work on all parts of his game.
“We’re going to get him down there and give him an opportunity to get things back on track,” Molitor said. “We don’t feel like we’re getting what we need from him, and he’s going to have to get down there and get to work.”
The corresponding roster move is expected to be Joe Mauer coming off the disabled list on Friday. He’s been out since May 19 with a neck strain and concussion symptoms.
Sano is hitting just .203 with seven home runs and 27 RBIs this season. He’s also made four errors in 37 games. Sano, an All-Star in 2017, has never played in more than 116 games in the majors due to injuries.
Last season, the Dominican Republic-born Sano slugged 21 home runs before the All-Star break but was hindered by injuries in the second half.
In December, a photographer alleged Sano grabbed her wrist and tried to pull her inside a bathroom at a store in a mall after an autograph session in 2015. Sano denied the allegations and MLB did not discipline him after completing an investigation into what happened.