Cain was not targeted in Sunday's 28-10 loss to the Ravens.
Cain had one catch for 35 yards in Pittsburgh's 16-10 win over Cincinnati on Sunday.
Cain could be utilized as the Steelers' third wide receiver Sunday at Cincinnati, Brian Batko of the Pittsburgh Post-Gazette reports.
Cain signed a contract with the Steelers on Saturday.
Cain cleared waivers and has signed with the Colts' practice squad, Tom Pelissero of NFL Network reports.
Cain was waived by the Colts on Saturday.
Cain didn't have catch despite two targets and playing 20 snaps on offense in Sunday's loss at Pittsburgh.
Cain is likely to be active for Sunday's contest against the Steelers, Zak Keefer of The Athletic reports.
Cain (coach's decision) is inactive for Sunday's contest against the Broncos.
Cain got the start at receiver opposite T.Y. Hilton in Sunday's win over Houston, but did not have have a reception or target.