If these three things go right, the Vikings can afford Stefon Diggs and Anthony Barr

Last summer, the Vikings kicked off an ambitious plan to retain the core members of their top-ranked defense, breaking with precedent in some ways and signing two veterans (Everson Griffen and Linval Joseph) to new deals when they still had two seasons remaining on their existing contracts.

Those deals were soon followed by an extension for cornerback Xavier Rhodes, and the Vikings signed linebacker Eric Kendricks to a five-year deal in April. Now, with defensive end Danielle Hunter signed to a five-year, $72 million contract, the Vikings have just one more key defensive player to lock up before next March (linebacker Anthony Barr), along with wide receiver Stefon Diggs.

General manager Rick Spielman said Wednesday the Vikings remain in conversations with both players' agents, and made it clear they'd like to retain both Diggs and Barr before each hits free agency in March. Hunter's deal, according to two league sources, includes a $15 million signing bonus, meaning $3 million of the bonus should hit the Vikings' books in 2018. That, combined with the still-to-be-signed contract of first-round pick Mike Hughes, should leave the Vikings with roughly $12.75 million in cap space left for 2018, with the ability to roll over whatever money they don't use this year in 2019 (they could push that to $13.55 million if they eventually release kicker Kai Forbath).

Assuming a $190 million salary cap in 2019, as Over the Cap does, the Vikings would have almost $32 million in cap space, not counting the deals for Hunter and Hughes. League sources said Hunter will get $48 million in the first three years of his deal; without seeing the full breakdown of the deal, let's assume, for now, that he'll average $11 million a season in base salary from 2019-2021. Hughes would have cap numbers of $2.24 million, $2.69 million and $3.13 million in that time. If Hunter has an $11 million average base salary and $3 million bonus proration from 2019-21, he'd carry an average cap hit around $14 million each year. Combine that with Hughes' contract, and we can work with an assumption that the Vikings have roughly $29.26 million in cap space left for 2019, counting what they'd roll over into next season. Let's put aside $2 million of that for expenses the rest of this season, and call it $27.26 million for 2019.

Can the Vikings get deals done with both Barr and Diggs, while still filling up the rest of their roster? The view here is yes — provided a few factors are in place. Here they are:

Productive negotiations that result in competitive — though perhaps not top-of-market — deals: If the Vikings gave Barr a deal that averaged, say, $11 million a season, he'd be among the four highest-paid 4-3 outside linebackers in the league. A deal for Diggs around $13.5 million a season would put him in the top 12 at his position, between players like Allen Robinson and T.Y. Hilton. If either player is intent on trying to climb much higher than that on the list, though, the Vikings might have a tough time retaining everyone — especially if they need to rework Adam Thielen's deal to keep him in line with Diggs. The Vikings often talk about their selfless, no-nonsense culture where winning is the only thing that matters; maintaining equilibrium gets a little trickier when there's big money involved. We'll see how things play out particularly with a player like Diggs, who's coming into a contract year after receivers hit the jackpot with new deals last spring.

Young players that can contribute quickly: There's a reason the Vikings were as aggressive in undrafted free agency as they were this season: In 2019, they're scheduled to have seven players — Kirk Cousins, Hunter, Rhodes, Griffen, Riley Reiff, Harrison Smith and Joseph — counting for at least $10 million against the cap. Barr and Diggs could be the eighth and ninth players on that list, respectively, with cornerback Trae Waynes on a fifth-year option of $9.069 million, tight end Kyle Rudolph counting for $7.625 million and Kendricks counting for $6.6 million. With a top-dollar quarterback, a pricey left tackle and a defense stocked with prominent players, it's hard for the Vikings to make room for many other expensive parts. Draft picks like second-rounder Brian O'Neill and fourth-rounder Jalyn Holmes could prove especially helpful if they can develop quickly, as could younger players like defensive tackle Jaleel Johnson, pass rushers Stephen Weatherly and Tashawn Bower and linebacker Ben Gedeon. Though Mike Zimmer sounded hopeful on Wednesday the Vikings could retain a player like defensive tackle Sheldon Richardson, it might be difficult to make the money work. Safety Andrew Sendejo's deal is up after 2019, and he's scheduled to make $5.5 million that season. Remmers, who might shift to guard this season, has a cap number of $6.35 million for 2019. At some point, something has to give, and young players might be able to help the Vikings weather some difficult decisions.

No surprises: The Vikings weren't able to enjoy their years of low quarterback costs once Teddy Bridgewater hurt his knee in 2016, forcing the team to trade for Sam Bradford. For the Vikings to make all this work and keep their young players, they can't afford many unexpected injuries or disappointing players that might force them to fill another hole with a veteran. That's a lot to ask, in the injury-ridden NFL, and things change quickly, but it would certainly help the Vikings to have a smooth year on the injury front after a couple rocky seasons health-wise. It's here we also should note the uncertain labor future of the league: the NFL's collective bargaining agreement expires after the 2020 season, a year before the league will renegotiate deals with its TV partners in the midst of an ever-shifting media climate. It would certainly help the Vikings if the deals they're doing now, and the ones they figure to try and finalize in the next few months, eventually exist in a world where cap ceilings and TV dollars continue to rise. That, of course, is far from a sure thing.