The Cubs made the move Friday, and optioned infielder/outfielder Micah Hoffpauir to Triple-A Iowa.
Soto, the NL rookie of the year last season, was in the lineup for Friday night's game at Colorado. He entered batting .230 with eight home runs and 27 RBIs in 69 games.
Koyie Hill had started all 26 games at catcher for the Cubs since July 7. He was the first Cubs catcher to start at least 26 consecutive games since Jody Davis started 38 straight in 1986.
Hoffpauir was batting .233 with eight homers and 25 RBIs in 81 games with the Cubs.