The injury to Foxworth, who broke into the league in 2005 with the Denver Broncos, occurred during a non-contact portion of practice on Thursday, according to a report posted on the Ravens' website (http://www.baltimoreravens.com/).
Foxworth appeared in all 16 of Baltimore's regular season games last season and had four interceptions and one fumble recovery.
The injury is the latest setback to Baltimore's backfield as Fabian Washington and Lardarius Webb are both recovering from knee injuries.
Harbaugh said there was a possibility that Washington and Webb could be ready when the team opens their season against the New York Jets on September 13.
(Writing by Gene Cherry in Raleigh, North Carolina; Editing by Frank Pingue)