Thomas (shoulder) was placed on the PUP list Friday.
The Ravens signed Thomas to a reserve/future contract Monday, Ryan Mink of the team's official site reports.
Baltimore signed Thomas to its practice squad Tuesday, Clifton Brown of the Ravens' official site reports.
Thomas was waived by the Bengals on Monday, Charlie Goldsmith of The Cincinnati Enquirer reports.
Thomas didn't have any targets in the Bengals' win over the Panthers, despite playing 22 offensive snaps.
Thomas failed to bring in his lone target while playing 24 of the Bengals' 53 snaps on offense in Monday's 32-13 loss to the Browns.
Thomas played on just four offensive snaps and failed to see a single target in Sunday's 30-26 win over the Saints.
Thomas played 41 offensive snaps in Sunday night's loss to the Ravens, catching one pass for 33 yards.
Thomas was on the field a lot more than expected in Week 1, following teammate Tee Higgins leaving with a concussion. Thomas had one catch for five yards, on five targets, while being on the field for 64 offensive snaps.