Cervelli left Friday night's game against St. Louis after breaking his hamate bone on a swing. He had surgery Saturday.
Cervelli is hitting .257 with 21 RBIs. Chris Stewart took over after Cervelli was hurt in the fourth inning.
Kratz is expected to join the Pirates for Saturday night's home game against the Cardinals.
The 35-year-old Kratz made his big league debut with the Pirates in 2010. He has also played for Philadelphia, Toronto, Kansas City and Houston.
Kratz went to spring training with San Diego this season and was traded to Houston. He played 15 games for the Astros, was cut in mid-May and joined the Angels' Triple-A team.
Right-hander Gerrit Cole also left Friday's game in the third inning due to right triceps tightness after giving up a leadoff single to Matt Carpenter. Cole will have an MRI on Saturday, Fox Sports reported.
"I'm all right," Cole said after the game. "I'll be fine."
The Pirates also designated for assignment Triple-A right-hander Trey Haley while left-hander Kyle Lobstein was optioned to Triple-A Indianapolis. Infielder Cole Figueroa was also optioned to Triple-A to make way for right-hander Arquimedes Caminero, who was activated off the disabled list.
Information from The Associated Press was used in this report.