Soto has not played since May 16 because of a tear in the meniscus in his left knee, which required arthroscopic surgery. He began his rehab assignment Monday.
"He's back into Spring Training mode where he needs to get some at-bats and figure it out," Cubs manager Dale Sveum said. "He wasn't swinging all that good before he got hurt. It'll be nice for him to make an adjustment."
Soto, who had hoped to return this weekend to the big league team, was batting .161 with three homers and six RBIs in 28 games before he was injured.