For two weeks, Davis dealt with a mysterious injury that couldn't be detected in medical tests. His reluctance to play triggered some criticism among fans.
Finally, a bone scan and MRI exam disclosed a stress reaction in Davis' lower left leg, and a Denver Broncos' orthopedic surgeon said the discovery is vindication for the running back.
Davis will wear a walking boot for three weeks, after which doctors will re-examine him. If they are satisfied he is completely healed, he could play again this season.
The Broncos (8-4) have only four weeks left in their regular season, although they could qualify for the playoffs.
Dr. Ted Schlegel said a stress reaction is an inflammation of the lining of the bone, which could develop into a more serious stress fracture if left untreated.
Davis missed most of the first eight games of the season with a severely sprained left ankle and foot, sustained in the season opener. He came back to play in games on Nov. 5 and 13, then missed the last two games with mysterious pain above his ankle.
The MRI exams did not detect any structural damage, neurological damage or blood clots.
Although his teammates and coaches rallied around him, Davis came under fire on sports talk shows from critics who accused him of being a malingerer and lacking toughness.
But a bone scan and another MRI exam Tuesday showed the damage.
"I think what this does for Terrell is, this vindicates what he's been telling us all along," Schlegel said Wednesday. "He has had significant pain, and he's been unable to practice and play. Unfortunately, we haven't been able to make a definitive diagnosis until we got this positive bone scan.
"So I guess in our minds, this is a positive for Terrell because he has been telling us all along that he has had significant pain, and now we have a reason for that."
Davis, the league's MVP in 1998 when he rushed for 2,008 yards, missed most of the 1999 season with a torn ACL in his right knee. He recovered steadily from that injury but went down in the season opener with the left leg injury.
Schlegel said the cumulative effects of those injuries would not have an impact on Davis' future.
The walking boot will enable Davis to immobilize the injured leg while he does cardiovascular exercises to keep himself in playing shape.
"We are confident, knowing Terrell's dedication and discipline particularly following his ACL surgery, that with his hard work the outcome will be positive," Schlegel said.
"The important thing is we caught this early. That will be helpful as Terrell recovers, because with it being a stress reation and not a stress fracture, we could expect the healing process to be a little quicker."
But Schlegel also acknowledged it was possible that Davis' season could be over.
Schlegel said the latest injury was caused by "some abnormal foot and ankle biomechanics that occurred due to his first injury. He's now completely recovered from the foot and ankle problem, but he has put extra stress on his lower leg the last two weeks, just from walking and running."
"We want to be aggressive right now with the boot and protection. We want this to completely heal before he is back playing," Schlegel said.
Davis was unavailable for comment, but coach Mike Shanahan said the diagnosis was a relief to Davis.
He also said the Broncos have declined to put Davis on injured reserve because of the possibility he could return this season.
"They say three weeks," Shanahan said. "It could be two weeks, it could be two months. There's a question of how much conditioning he can do with that thing on his leg.
"We're going to wait and see. We're not going to put him on IR unless we know that he definitely can't go because we know what a big-time playmaker he is. If he can help us down the stretch, we want him there."
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