The 37-year-old Grilli has struggled with his command this season and is 0-2 with a 4.87 ERA and 11 saves in 22 appearances. But he was pivotal to the Pirates’ resurgence last year, when he piled up 33 saves and had a 2.70 ERA in helping the club to a 94-68 record.
Grilli is expected to join the Angels in Kansas City on Saturday.
Frieri had a career-best 37 saves for Los Angeles last year, but the 28-year-old right-hander is just 0-3 with 6.39 ERA and 11 saves in 34 appearances this season.