Soto has not played since Friday because of a mild ligament sprain in his right shoulder. He was in Monday's lineup against the Giants but scratched after feeling some discomfort in batting practice.
Lee left the team Monday to drive to Sacramento to be with his grandfather, who was ill.
Castillo was batting .251 in 65 games at Triple-A Iowa with 13 home runs and 57 RBIs. Hoffpauir was hitting .273 with 20 homers, 32 doubles and 87 RBIs in 107 games.
The Cubs added another rookie to the bullpen Monday, recalling right-handed pitcher Marcos Mateo from Iowa and optioning right-hander Mitch Atkins to the Minor League team. Mateo, who has a 1.90 ERA in his last 20 Minor League appearances, made his Major League debut Monday and took the loss in the Cubs' 4-3 loss to the Giants.
In 25 appearances this season with Double-A Tennessee and Iowa, he was 0-1 with a 3.24 ERA.
The Cubs also will be without manager Lou Piniella for this four-game series. Piniella flew to Tampa, Fla., on Sunday night to be with his mother, who was ill.
"It's been a tough year for him, but I was hoping to see him and get a chance to talk to him," Giants manager Bruce Bochy said. "I know this is his last year. I like Lou a lot and respect him and have gotten a chance to know him quite well and he's a good man."