Seattle coach Jim Mora said Monday that further tests on the three-time Pro Bowler's chest muscle indicated a partial tear rather than the complete one doctors told him Tatupu had the day before.
"After further review and further imaging, we're not certain yet Lofa is done. They did an MRI test, and it doesn't look like the muscle and tendons are completely detached from the bone," Mora said, one day after Tatupu got hurt in Seattle's 27-3 loss to Arizona and was then declared out.
"So that might have been a little premature ... we'll keep our fingers crossed there."
Mora said team medical personnel are now examining Tatupu's relatively healthy pectoral muscle on the right side, including with another magnetic resonance imaging test. They will compare it with images taken on the injured left one to further gauge how much damage the left pectoral sustained.
If Monday's results from the MRI are proven accurate, the team's co-captain could be back after a few weeks of rehabilitation -- though it appears he will miss at least Seattle's next game, at Dallas on Nov. 1. The team may have a timetable on his return before it leaves for a bye weekend break following Wednesday's practice.
"It was pretty grim [Sunday]. So we got good news," Mora said. "Sometimes it goes the other way, so it was nice to have the good news."
Seattle (2-4) has had 12 starters miss a combined 35 games through the season's first six weeks.
Tatupu, whom Mora calls incomparable as the "axis of communication" inside the defense, was injured while trying to tackle Cardinals receiver Larry Fitzgerald following a reception over the middle in the second quarter Sunday. He appeared to get hit by teammate Deon Grant on the play, awkwardly twisting his upper body.
Two team doctors and three trainers attended to Tatupu briefly on the bench.
A doctor pressed on Tatupu's left shoulder, and the linebacker reacted with a painful jerk. He was then taken into the locker room and returned wearing sweats in the second half.
Tatupu still had a team-high eight tackles against the Cardinals. David Hawthorne replaced him, the second time this season the undrafted free agent from 2008 has filled in at middle linebacker.
Hawthorne made his first career start last month and played nearly two full games after Tatupu was slowed with a hamstring injury. Veteran D.D. Lewis will now back up Hawthorne.
"Hawthorne has showed he can fill those shoes. I'm going to make sure to have his back and if he needs me all he has to do is keep his ears open. I'm going to be right there for him," Grant said. "We'll be all right, [but] we're going to miss Lofa big time because he's more than a leader on this defense. He brings a lot of passion."