To make room for Clausen on the roster, the Ravens placed quarterback Joe Flacco on injured reserve Tuesday.
Flacco tore the ACL and MCL in his left knee Sunday in a 16-13 win over St. Louis and is lost for the season. Schaub will be the starter on Monday night at Cleveland.
Clausen was waived by the Bears on Monday. He played in two games with Chicago this season, starting once.
The six-year veteran was chosen by Carolina in the second round of the 2010 draft after playing college ball at Notre Dame.
Clausen has played in 19 games, starting 12. He has five touchdown passes and 11 interceptions over his career.
AP NFL website: www.pro32.ap.org and http://twitter.com/AP-NFL