An MRI exam Monday showed that Favre sustained two fractures near his surgically repaired left ankle and heel, but another surgery isn't required. Favre, who wore a support boot Monday, said Sunday that he wouldn't play against the Patriots if he believed he would negatively impact his team.
Favre, 41, has started in an NFL-record 291 consecutive games. If he can't practice this week, that streak likely will come to an end.
As for Jackson, the one-time Vikings starter took the majority of snaps during offseason workouts and training camp while Favre recovered from his ankle surgery in Mississippi. Jackson also has taken increased reps during the past few weeks because Favre has suffered from tendinitis in his throwing elbow.
If this week leads to another opportunity, Jackson insisted Monday that he's ready for it.
"I've been working hard throughout this whole process, and I'll continue to work hard," Jackson said. "Now it's about continuing to go out there and make plays."
Can a quarterback actually improve when all he does on the weekends is watch?
"Oh, yeah," Jackson said. "I feel like I've improved a lot in the last year-and-a-half watching Brett. I feel like I've come a long way, probably the farthest I've come from year to year, even though I didn't play a whole lot."
Specifically, Jackson said he has a stronger grasp of pass-protection concepts and how to quickly read his blockers, his receivers and the defense before deciding where and when to throw.
"I'm not Brett, and I understand that, and a lot of the stuff that he sees I probably won't see," Jackson said. "But I'm a different player. I can move around a little bit more. Good things will come my way. I know I'm not going to go out there and operate the same way he's going to operate, but I feel like I've learned a lot from him. I'm not going to try to be him. I learned a lot from him that will help me play and be better."
Jackson spoke confidently, almost as if he already has assumed the role. Given Favre's body language during and after last Sunday's loss at Green Bay and Childress' diagnosis of the injury Monday, Jackson's return to the lineup hardly would be a shock.
But given Favre's history of high pain tolerance and the competitive drive that has helped make him famous, it hardly would be a surprise if he started Sunday.
"Brett, he's a warrior, so I'd be real surprised if he don't play," Jackson said, "but I'm going to be ready to play if my number is called."
After two starts as a rookie in 2006, Jackson was given the job in 2007. Even with the emergence of then-rookie running back Adrian Peterson to help keep defenses from focusing only on the passing game, Jackson often looked erratic and overwhelmed. Despite an 8-4 record as a starter that year, missing four games because of a variety of injuries, Jackson threw just nine touchdown passes and never cracked the 250-yard mark.
Jackson took the job back later that year after Frerotte was hurt, but after a solid stretch in December, he was harassed by the blitz-happy Philadelphia Eagles in the first round of the playoffs, a defeat that ultimately triggered the Vikings' first pursuit of Favre. The Vikings went back to get Favre again this year, too.
Jackson, who will be an unrestricted free agent after the season, said he's not trying to prove himself at this point.
"I'm not looking forward to next year right now. Just try to do our best right now. Just try to win a Super Bowl this year," said Jackson, whose career record in 20 starts including one postseason game is 10-10.
Jackson, an unpolished product from small-school Alabama State, came to the NFL as a second-round draft pick in need of plenty of development time. Perhaps he's a late bloomer or maybe he will never flourish, but if Favre is hurt badly enough to rest Sunday, Jackson will have the chance to prove one theory or the other.
"Hopefully it translates to the field, but this is the best I ever felt," Jackson said.
His teammates were consistently supportive of him before Favre's arrival last year, and if Jackson indeed takes over, there likely won't be much public skepticism coming from the Minnesota locker room.
"We've got nothing but utmost confidence in him," defensive tackle Kevin Williams said.
The Associated Press contributed to this report.