IRVING — The Dallas Cowboys suffered another blow on Thursday when nose tackle Jay Ratliff underwent possibly season-ending surgery Tuesday to repair a sports hernia.Ratliff, 31, has already missed seven games this season, including the past three with a groin injury. He was no closer to getting on the field Sunday against Pittsburgh and opted to fly to Philadelphia for the surgery.Ratliff has yet to be placed on injured reserve. But its unlikely he will be able to play again this season. The Cowboys have three games left and must sweep them all to have a shot at the playoffs.Ratliff, who missed the first four games of the season with a high ankle sprain, becomes the fifth defensive starter to be sidelined for the season with injury -- joining linebackers Bruce Carter and Sean Lee, safety Barry Church and defensive end Kenyon Coleman, who are already on injured reserve. Add in nickel cornerback Orlando Scandrick and the Cowboys defense is without six primary contributors.Ratliffs surgery further complicates an already compromised situation at nose tackle, considering that his primary replacement, Josh Brent was placed on the reserve non-football injury/illness list on Wednesday. Brent is facing intoxication manslaughter charges as a result of last Saturdays one-car accident that killed practice squad-linebacker Jerry Brown.Sean Lissemore moved over from defensive end to start at nose tackle against Cincinnati last Sunday. He will start against Pittsburgh. Robert Callaway, signed off the practice squad last Saturday, and Brian Schaefering, who signed off the street on Wednesday, will be the backups.Ratliffs surgery comes less than two weeks after he had verbal altercation with owner Jerry Jones in the locker room following the Philadelphia game. Jones reportedly told Ratliff we need you and he took offense, thinking his desire to play was being questioned.Ratliff got in Jones face and said some derisive things before being pulled away.Jones has since called it a regrettable situation where the emotions of the game to the best of both parties.Time will tell if the events of the past two weeks dont impact Ratliffs future with the Cowboys, who might be facing a decision of whether to release him or bring him back for a ninth season in 2013.Ratliff had 25 tackles, one tackle for loss and 10 quarterback pressures in six games this season with no sacks, marking a decline in his sack numbers for a fifth straight season. Ratliff signed a five-year extension for $40 million in 2011, with $17.5 million guaranteed. He is set to count $7 million against the cap next season.