The 2017 NFL regular season couldn't have gotten off on a much better foot for Minnesota Vikings rookie running back Dalvin Cook. Through Week 3, he ranked second in rushing yards while also sitting among the top 10 in fantasy football scoring at his position.

His upside moving forward also looked great when considering he was a workhorse for the Vikes -- he had played in better than 70% of the team's offensive snaps, along with handling 70.1% of rushing attempts during this span.

Cook was on his way to another strong performance in Week 4 against the Detroit Lions, too. The rookie had accumulated 66 yards and 1 touchdown off 13 carries, but everything went downhill once he suffered a scary non-contact knee injury early in the third quarter. After undergoing an MRI, head coach Mike Zimmer has confirmed the worst possible news -- Cook suffered a torn ACL that will effectively end his season.

This news is obviously terrible for Cook, as his explosive introduction to the NFL had been fun to watch. It does have some serious implications with regard to fantasy football, as well.

Impact on the Vikings' Backfield

As mentioned before, Cook had been the true workhorse in Minnesota's backfield prior to his injury, with Jerick McKinnon (26 rushing yards on 8 carries and 30 receiving yards on 8 catches through Week 3) and Latavius Murray (17 yards on 7 carries with no targets) largely being non-factors. But outside of the production, McKinnon was the clear second option here -- he appeared on the field for double-digit snaps in all three games with Cook healthy, while Murray never played more than eight snaps in a game.

McKinnon also spent some time on the sideline with an ankle injury Sunday, but he did eventually return, giving us nearly two quarters worth of Cook-less Minnesota football to get a feel for how the backfield will operate moving forward. And what stands out the most is that McKinnon's role didn't change much.

He was out-snapped 20-5 by Murray following Cook's injury and didn't notch a single a touch during that time.

Meanwhile, Murray immediately became a factor by garnering two targets and seven carries despite the Vikings being forced into a pass-heavy game script since they were playing from behind in the fourth quarter.

While Murray's 0.00 Rushing Net Expected Points (NEP) per carry through three games isn't spectacular, it's better than what McKinnon had produced prior to Week 4 in nearly the same number of carries (-0.74). And although it's difficult to make a direct comparison between these two because they played for two different teams in different situations, Murray has finished ahead of McKinnon in Rushing NEP per carry in two of the last three seasons.

It wouldn't be surprising to see McKinnon be a popular option off the waiver wire -- his passing-game usage with Cook healthy was encouraging. However, it looks like Murray will get the biggest boost in volume. If we combine that with his superior efficiency as a rusher, he's appears to be the better back to own in Minnesota at the moment.

Where to Look for Replacements

With Cook's diagnosis confirmed, he can safely be dropped in fantasy football leagues since he won't be back until next season. Having quickly established himself as an every-week starter, this kind of loss to injury means there's a bit hole at running back that likely needs to be filled via the waiver wire. Murray makes sense as being a strong candidate to add, but what about guys who aren't on Minnesota's running back depth chart?

Adrian Peterson's role in the New Orleans Saints backfield keeps declining each week, and he played in just six snaps during their Week 4 blowout win over the Miami Dolphins. Alvin Kamara -- who is currently available in 54% of Yahoo! leagues -- was on the field for 35% of the Saints' snaps, which was his second-highest mark of the season. That's significant considering his usage primarily comes in the passing game and New Orleans' 20-0 drubbing of Miami would generally bring about a run-heavy game flow. He also leads the Saints' backfield in fantasy points per snap, giving him huge fantasy appeal based off his increasing workload.

Ty Montgomery made an early exit because of a rib injury Thursday night, and with Jamaal Williams potentially missing some time himself with a knee injury, Aaron Jones -- who is available in 89% of Yahoo! leagues -- could become the clear-cut leader in the Green Bay Packers' backfield. Montgomery's injury isn't thought to be overly serious, so Jones won't be able to fill that hole in your lineup for the whole year. If he draws a start or two while being the lead back in a strong offense, though, he'll be a worthy stop-gap player while you look for a longer-term solution.

Another potential option is Wayne Gallman of the New York Giants, who is available in 97% of Yahoo! leagues. Paul Perkins entered Week 3 with a -0.29 Rushing NEP per carry (the second-lowest mark among backs with at least 15 carries), while his 8.7% success rate -- the percentage of carries that generate a positive NEP -- was the lowest of that group by over 10%. He also went down with a rib injury over the weekend, leading Gallman to play a team-high 39% of New York's offensive snaps.

The x-rays on Perkins came back negative, but if he's forced to miss any time, Gallman could step in as the lead back. With Perkins' awful start to the year, this could be his chance to prove himself and earn extended playing time no matter the situation, potentially giving him some long-term fantasy upside.

Cook's injury is unfortunate and his early-season production will be tough to replace, but there are at least a few options available on the waiver wire worth investigating for both the short and long term.