Watching Marcus Tubbs roll in pain on the turf at Qwest Field on Thursday night, it was hard not to think the season was over for the oft-injured...

Watching Marcus Tubbs roll in pain on the turf at Qwest Field on Thursday night, it was hard not to think the season was over for the oft-injured Seahawks defensive tackle.

And that turned out to be exactly the case. Tubbs likely will be out for the season after tests Thursday night and Friday revealed a torn anterior cruciate ligament in his right knee, according to sources.

This injury is just another hard-luck chapter in Tubbs’ once-promising career.

Tubbs had a magnetic resonance image of his knee taken Thursday after Seattle’s 19-14 exhibition victory over the Oakland Raiders. He hurt the knee late in the first quarter on a running play.

Tubbs had more tests on the knee Friday but it didn’t appear the original diagnosis would change, sources said.

The length of time to recover from and rehabilitate such an injury is about six months, depending on the severity. That would cost Tubbs the season for sure, and likely means he will be placed on injured reserve, making him ineligible to play at all in 2007.

The Seahawks did not confirm Tubbs’ status or the test results, but are expected to do so today when they announce final roster cuts.

The loss of Tubbs is a major blow to a Seahawks defense hoping to improve. Tubbs returned to practice Aug. 14 after left knee surgery. Last Saturday, in an exhibition game against Minnesota, he saw his first live action since last October.

The Seahawks were trying to be careful with Tubbs after his last knee injury and limited him to a handful of plays in the Minnesota game. Tubbs wasn’t going to play much in the Oakland game either, but misfortune struck early.

Defensive teammates lauded Tubbs for his athleticism and coaches loved his knack for stuffing running plays up the middle. At 6 feet 3 and 320 pounds, the former first-round choice from Texas was adept at taking up space and forcing two offensive linemen to block him, which freed up linebackers like Lofa Tatupu and Leroy Hill to get to ball carriers.

In the five games Tubbs played last season — he has never played every game of an entire season — the Seahawks allowed 65 fewer yards per game and almost a full yard fewer per rush compared to the 11 contests without him.

“He’s the biggest body we’ve got on the defensive line, and we’re going to need that,” defensive end Bryce Fisher said last week.

Now the Seahawks are going to need to compensate for Tubbs’ loss. Only backup defensive tackle Russell Davis has comparable size, and he isn’t a lock to make the final roster, though his chances probably increased.

The starters at defensive tackle are Chuck Darby and Rocky Bernard, two solid interior linemen recognized more for their pass-rushing skills. Rookie Brandon Mebane, a third-round choice, was brought in to be a run-stuffing tackle and likely will get more playing time now.

Tubbs has had arthroscopic knee surgery, Achilles surgery, a high ankle sprain and a hamstring injury in his short pro career. But he felt his left knee would hold up and he was working his way back into playing shape.

“The injury bug has prevented him from reaching his potential on the field,” coach Mike Holmgren said after the game Thursday. “I feel bad for him.”