Pro Bowl defensive tackle Haloti Ngata, the key to the Ravens' run defense, missed practice Thursday after being limited the day before.
Ngata is officially listed with a shoulder injury. But the three-time Pro Bowl player has also been dealing with a minor injury to his medial collateral ligament in his right knee.
He's been less than full strength for weeks but still played against Dallas and Houston before last week's bye.
Ngata has been one of the more durable defensive linemen in the league, playing in 46 straight games. The last time he was sidelined was November 2009, when the Ravens played at the Browns. The Ravens travel to Cleveland on Sunday to face the Browns and rookie running back Trent Richardson.
If Ngata can't play, the Ravens could opt to start Terrence Cody, who was benched this season as the team's starting nose tackle. Ma'ake Kemoeatu, the starting nose tackle this season, has a knee injury but he's been a full participant in practice all week.