The move involving Perez is retroactive to Monday.
Also on Tuesday, the Orioles recalled left-hander Bruce Zimmermann from Norfolk and optioned right-hander Chris Vallimont to the Triple-A club.
McCann, 33, landed on the injured list with a sprained left ankle on June 18.
In his first season with Baltimore, McCann is hitting .194 with three homers and seven RBIs in 31 games as Adley Rutschman‘s backup. In 10 seasons with the Detroit Tigers (2014-18), Chicago White Sox (2019-20), New York Mets (2021-22) and Orioles, he is a .241 hitter with 81 homers and 323 RBIs.
Perez, 27, is nursing left forearm soreness.
He is 2-1 with a 4.45 ERA in 33 relief appearances this season. He is 11-5 with one save and a 3.76 ERA in 144 career relief appearances with the Houston Astros (2018-20), Cincinnati Reds (2021) and Orioles.
Zimmermann, 28, is 1-0 with a 6.10 ERA in five relief appearances.
Vallimont, 26, allowed one hit in two-thirds of a scoreless inning in his major league debut Monday. He did not receive a decision.
Orioles activate C James McCann, put LHP Cionel Perez on IL