Affeldt had been on the disabled list since April 17 batting a strained muscle in his right side. The veteran reliever struggled in his first six appearances out of the bullpen this year, posting a 5.79 ERA in 4.2 innings of work.
San Francisco cleared room for Affeldt on Wendesday when they optioned right-handed pitcher Sandy Rosario to Triple-A. Rosario had only made one appearance and faced one batter for the Giants during his stay, recording an groundout against Martin Prado.
Peguero has hit well in Triple-A this season, hitting .415/.433/.585 over 67 plate appearances this season. The 24 year-old outfielder is considered one of the top prospects in the Giants farm system, as he flashes above-average speed and the ability to make consistent contact at the plate. Peguero received a brief amount of playing time for the Giants last year, hitting .188/.188/.188 in 16 plate appearances.
Sanchez has struggled at the year, hitting .150/.261/.150 over 23 plate appearances. Guillermo Quiroz will now serve as the team's primary backup catcher behind Buster Posey; Quiroz is batting .375/.500/.500.