The Vikings kept on rolling in the first few weeks after Adrian Peterson, their seven-time Pro Bowl running back, underwent knee surgery on Sept. 22, a few days after he was hurt in their big Week 2 victory over the Green Bay Packers.

With Peterson resting the surgically-repaired lateral meniscus in his right knee, they racked up three more wins to get to 5-0 and at one point were the NFL’s lone unbeaten team. Their first loss came 31 days after Peterson’s knee surgery.

Then came the free fall to 6-6.

As the Vikings were preparing for their latest loss, last Thursday’s 17-15 defeat against the Dallas Cowboys, they got a glimmer of hope when Peterson was cleared to start running, his next hurdle to a potential comeback.

Last Tuesday, after media spotted Peterson sprinting on the side of a practice, coach Mike Zimmer said he didn’t know if Peterson was close to returning.

“He’s doing good,” Zimmer said. “He’s probably ahead of schedule, I guess.”

But with the team’s once-promising season on the brink and another staredown over his contract looming in the offseason, does it even make sense for Peterson to return to action if his knee isn’t completely healed and put himself at risk?

The Vikings declined to make Peterson available for this story. But a trio of analysts who worked in the NFL — a former team doctor, an ex-agent and a former team president — provided a glimpse into the decisionmaking process that a team and player must navigate before he is activated from injured reserve.

The first question that must be answered: Will doctors clear Peterson to play?

In the days after his right leg twisted in the turf at U.S. Bank Stadium, Peterson mulled whether to get the meniscus trimmed or fully repaired. A trim would have gotten him back on the field sooner, but ultimately the 31-year-old opted to get the tear repaired, lessening the risk of reinjury.

Since then, Peterson and the Vikings have eyed a return in mid-to-late December.

Dr. David Chao, physician for the San Diego Chargers from 1997 to 2013, said the biggest key to a player recovering from a meniscus repair is that “the meniscus needs time to heal.” At minimum, a player typically needs three to four months to heal “and it could easily be six months,” he said.

The three-month anniversary of Peterson’s surgery is Dec. 22, two days before the Vikings travel to Lambeau Field to play the Green Bay Packers in Week 16.

“It’s hard to speed up biology,” said Chao, who in a phone interview last week spoke generally about meniscus injuries because he has not examined or treated Peterson. “You can be the quickest healer in the world, but biology is biology.”

Peterson is inching closer to a potential return after being cleared to run, but Chao cautioned that a player “running on the sideline is a ways from football still.”

Chao said if someone were to play on the injury before it is fully healed, there is a possibility the meniscus could be torn again or simply not heal. And long-term implications of a torn meniscus could include arthritis in the injured knee.

But if a player has rehabbed well and has no strength or functional deficits, Chao said, there should not be significant risk of damage to other structures of the knee, such as the anterior cruciate ligament or the medial collateral ligament.

Chao said team doctors and head athletic trainer Eric Sugarman, who must deem Peterson in shape and ready to go from a football standpoint, are not the only ones who have a say in deciding whether Peterson will suit up again in 2016.

“Return to play is a three-part decision,” Chao said. “Most people think that decision is simply, ‘Well, what did the doctor say?’ It’s really not that simple.”

The team’s football staff, led by General Manager Rick Spielman and Zimmer, must decide whether the potential boost that Peterson might bring to the league’s 32nd-ranked offense is worth the risk of him getting reinjured.

And Peterson also has to give the thumbs-up before he returns to the field.

“The player needs to sign off on it, and that includes his agent, maybe his wife, maybe his dad,” Chao said, still speaking generally. “They could say: ‘No. No. No. This is a contract year and we want to be 100 percent. It’s not worth it.’ ”

The matter of money

The way that Peterson has attacked his rehab in recent weeks suggests that he still plans on returning this season — but reinjuring his knee could cost him.

On the new three-year deal he signed in the 2015 offseason — after he missed most of 2014 because of a suspension, then engaged in a Cold War of sorts with the team — Peterson is scheduled to have a salary cap number of $18 million next season.

But none of the money in the deal’s final year is guaranteed. So the Vikings can move on from him with no financial repercussions if they choose. They owe Peterson a $6 million roster bonus on the third day of the 2017 league year in March, so they will need to make a decision on his status before then.

If he rushes back and reinjures his knee, the decision could be made for them.

That lack of security could give Peterson pause as he works his way back to a team that could be eliminated from playoff contention before he pulls a purple jersey back on. But Joel Corry, a former player agent who now writes about the business of football for CBS Sports, says Peterson still has incentive to return.

“He didn’t leave a great impression around the league in the couple of games he played before the injury,” Corry said. “If he comes back and is the one who gets them over the hump and into the playoffs, that helps him immensely.”

In the two games before tearing his meniscus, Peterson averaged 1.6 yards per carry and did not find the end zone. However, his replacements, Jerick McKinnon and Matt Asiata, have not fared much better behind an offensive line that has been decimated by injuries. The Vikings rank last in the NFL in rushing.

Corry said that by returning to the field and running better than he did in September, Peterson can prove to the Vikings that he is “still worthy of being a high-price player” and also “showcase himself” to others in case they disagree.

“He kind of has to show that the knee is all right. He’s a 31-year-old running back and he’s already had [a significant injury to each knee],” Corry said. “It’s different if teams actually see him and can say, ‘OK, he looks healthy,’ as opposed to wondering what he would look like having not seen him play since the injury.”

Thinking for the future

Given Peterson’s age, injury history and that he is the only NFL running back with an average annual salary over $10 million, the Vikings must consider this winter whether they still can afford to pay him $18 million. The addition of quarterback Sam Bradford’s cap hit of $17 million to $18 million also complicates their cap situation.

Corry suggested the Vikings could consider extending Peterson’s contract for another year or two, which would lower his cap number for 2017 but likely incur financial risk for future seasons. He noted that not many running backs remain effective as they run toward their mid-30s, but “he’s defied the odds before.”

But Joe Banner, who worked in the Philadelphia Eagles front office from 2005 to 2012 before a brief stint with the Cleveland Browns, believes the Vikings either have to persuade Peterson to take a pay cut for 2017 or simply release him.

During his time in the NFL, Banner saw some proud players react emotionally to requests to take a pay cut and ultimately opt to sign elsewhere for less money.

“Frankly, that would be totally in the hands of Adrian and his agent,” said Banner, now an analyst for ESPN. “If Adrian felt it was really important to him to finish his career in Minnesota, and he felt they had a long way to go next year, and he felt like he could get close to market value in Minnesota,” he could agree to a pay cut.

But, Banner said, the Vikings, who may need to win out to make the playoffs this season, can worry about 2017 in 2017. If and when Peterson is ready and willing to play, they should play him.

“I don’t think it’s a situation where you can start worrying about the implications of next year while you’re still in the middle of the race,” Banner said. “When you have a player of this caliber and you’re still in the mix and you’re paying him, if he’s capable of getting back on the field, you get him back on the field.”