Coach Mike Holmgren announced Darby, a three-year starter and leader of Seattle's defense, tore the patella tendon in his right knee Sunday night. Darby was being blocked on a running play in the second half of a 28-17 loss to New Orleans when his knee buckled.

"Now those injuries, according to the doctors, they fix him and he continues playing," Holmgren said. "But it's a sixth-month deal."

Holmgren said Brandon Mebane, a rookie third-round draft pick from California who has played in all six games this season, will start Sunday when the struggling Seahawks (3-3) host winless St. Louis. The coach also said the team will be trying out veteran defensive tackles this week looking for depth.

Depending on how well Mebane plays, Darby could have played his 36th and final game for Seattle. The seventh-year veteran turns 32 next week and is not signed beyond this season. He is in the final year of a contract that is paying him $1 million in base salary for 2007.

There is precedent of a comeback from this injury. Former Seahawks' Pro Bowl center Robbie Tobeck, now retired, had a similar surgery on his knee before the 2000 season. He missed the first 12 games before returning for that season's final month — then didn't miss a start for the next 5 1/2 years.

This is Seattle's second season-ending injury to a leader in as many weeks. Pro Bowl fullback Mack Strong was forced to retire because of a herniated disk in his neck that was pinching his spinal cord.

"There is a toll ... both Mack and Chuck were absolute leaders to the offense and defense," Holmgren said. "High-character, high-effort guys.