This will be Rizzo's second stint with San Diego after he originally was recalled and made his major league debut on June 9. He was optioned back to Tucson July 22 when he hit just .143 with one homer and six RBI in 35 games as the starting first baseman.
Padres manager Bud Black said Rizzo will share first base duties with 27-year-old rookie Jesus Guzman, who is batting .306 with five homers and 37 RBI in 60 games.
Rizzo, 22, was one of the two prospects San Diego acquired in a December trade with Boston when they dealt All-Star first baseman Adrian Gonzalez.
In his two stints with Tucson, Rizzo hit .331 with 26 home runs and 101 RBI in 93 games.
San Diego also recalled infielder James Darnell from Tucson. Darnell made his major league debut on Aug. 9.