Lacey suffered a subluxation of his left knee cap in last week's loss to the Arizona Cardinals.
Playing his fourth season out of Oklahoma State, he posted 36 tackles, four passes defensed and an interception in 11 games.
To take Lacey's spot on the roster, the team signed cornerback Ron Bartell.
Bartell is an eight-year veteran and had spent six games with Oakland this season before getting cut on Dec. 10.
