Brett Favre has a stress fracture in his left ankle that could end the Minnesota quarterback's NFL-record durability streak at 291 consecutive games started.
Vikings coach Brad Childress said Monday an MRI on Favre's foot revealed the fracture and an "avulsion" fracture in the calcaneus, which is the heel bone. An avulsion fracture occurs when a fragment of bone is torn away by a tendon or ligament.
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Favre had arthroscopic surgery on the ankle in May, and he received a series of lubricating injections in the joint at the beginning of the season. The ankle has bothered him at times this fall, but he hurt it in Sunday's 28-24 loss at Green Bay as he was being tackled from behind while throwing his first of three interceptions against the Packers.
The 41-year-old Favre was limping around during the game and walking gingerly afterward, and Childress said he was wearing a walking boot around the practice facility on Monday to make him more comfortable. He refused to rule Favre out of Sunday's game at New England, but he also insisted that the streak won't influence the decision on whether to play him against the Patriots (5-1).
"He's got to be able to do all the things that his position does," Childress said. "You can't put a guy that's a sitting duck out there. His competitive nature I'm sure will come into it. But a lot of times you've got to protect people from themselves."
The Vikings (2-4) are struggling to find the groove they enjoyed in Favre's first season, which started 6-0 and ended in the NFC championship game. With Favre's turnover count now at 14 - including 10 interceptions, already three more than last year - he has been hurting them as much as he's helped them so far.
Favre didn't enter the locker room at Winter Park when it was open to reporters on Monday, but after the game he said he wouldn't put his record ahead of common sense.
"If I can play but not be effective, then it's not worth playing," Favre said. "I hope I use good judgment, so we'll see. I'm no spring chicken anymore. I don't heal as quickly. I know the heart's in the right place, though. I know I left it on the field. It's just disappointing that it didn't work our way."
Favre is also the subject of an NFL investigation into allegations that he sent lewd photographs and suggestive messages to a female New York Jets employee in 2008. Favre met with an NFL security official last week but has not publicly addressed the allegations, which were posted on the Deadspin website.
League spokesman Greg Aeillo said Monday there was nothing to report about the investigation.