GREEN BAY – If you’re looking for a reason why the Green Bay Packers’ free-agent shopping spree ended on the first day free agents could sign contracts, and why the team has been telling people they’re tight against the salary cap despite having nearly $9 million of room, look no further than No. 97 on their roster.

If they do nothing else the rest of the year, they must make sure they have enough salary-cap room to sign nose tackle Kenny Clark to a long-term extension.

Clark has played just three seasons for the Packers and won’t become an unrestricted free agent until after 2020, provided the club exercises a fifth-year option it holds. The Packers have until May 3 to do so, but it’s such a sure-thing that they might have sent the letter to him already, making it official they will hold his rights for the next two years at the very reasonable price of about $9 million total.

Clark is due $1.726 million this year and will receive somewhere between $7-8 million in ‘20 per the option-year rules under which all first-round draft picks are subject. It’s almost too good to be true to have a player with so much potential under contract for so little.

Nevertheless, the Packers should try to take advantage of the leverage they have and see if they can lock down Clark for five to six more years, guaranteeing they’ll have him during the prime of his career. History shows that teams that make an early financial commitment with proven first-round talent mostly hit home runs.

Clark is that proven talent.

Just 23, he already qualifies as one of former general manager Ted Thompson’s best first-round picks and if his upward trajectory continues he could eventually move past Clay Matthews into the No. 2 spot. Set to enter his fourth year in the NFL, Clark isn’t a superstar the caliber of J.J. Watt or Patrick Peterson.

But he’s going to be critical to the Packers’ success in the coming years.

Last year, he finished second on the team in sacks (six) and quarterback pressures (10), third in tackles (73), tied for third in quarterback hits (three) and fifth in defensive snaps played (722) despite missing three games with an elbow injury.

He has a personal story that easily could have gotten the best of him, yet he carries himself like a 10-year veteran. He is one of the most well-liked players in the locker room and has accomplished more on the field before his 24th birthday than many do in a career. And he plays a critical position in the middle of the defense.

As one agent who has represented first-round picks said, “He’s a unicorn.”

Given the Packers don’t have a lot of salary-cap room – and were contemplating using some of it on Arizona Cardinals unrestricted free agent defensive lineman Rodney Gunter, who visited the team Wednesday – they have reason to wait. They can let Clark play this year out and still have all next offseason to negotiate with him.

But they also know that he has just scratched the surface and every year he progresses, his price tag rises with him. If he makes the Pro Bowl next season, the Packers will have to pay him considerably more than they would now, and he could conceivably play out 2020 and force the Packers to use a franchise tag of around $16-18 million just to keep him.

As the agent said, this is the only time the Packers will have some leverage with Clark, so why not use it? In Clark’s favor, he could take in somewhere between $25 million-$35 million in guaranteed money this year and take away the risk of playing without a big contract the next two years.

Since 2011, when the fifth-year option was first put into place under the new rookie wage scale, most of the first-rounders whose options were exercised had to wait until after their fourth season to sign a long-term deal. Only a handful of teams signed first-rounders before their fourth season began.

Here’s how the rules work:

First-round picks sign four-year deals like every other draft pick, but the club has the option to add a fifth year provided it declares its intention before the player’s fourth season. The fifth-year salary is based on veteran salaries of players who play the same position.

If you were selected in the first 10 picks, your option-year salary would be equal to the average of the 10 highest salaries at your position. Picks 10 through 32 receive the average of the third through 25th highest salaries at their position.

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Last year, a defensive tackle picked at Clark’s spot received a fifth-year option of $7.1 million. The offer is guaranteed for injury as soon as it is exercised and becomes fully guaranteed the following March, so Clark knows he’s going to get that money.

But there’s a big difference between $7 million and $30 million.

If the Packers want evidence that it pays to invest early in emerging stars, they only need to look at those teams who inked deals before the start of the player’s fourth season.

Since the ’11 draft, 10 players have signed long-term extensions at the point Clark is at in his career.

Here’s the list:

2011 draft – Cardinals cornerback Patrick Peterson, Cowboys tackle Tyron Smith, Texans defensive end J.J. Watt, Rams end Robert Quinn.

2012 draft – Dolphins quarterback Ryan Tannehill, Panthers linebacker Luke Kuechly.

2013 draft – Chiefs tackle Eric Fisher, Eagles tackle Lane Johnson, Bears guard Kyle Long, Cowboys center Travis Frederick.

The only deal among those that was a bust was Tannehill’s. He never became the quarterback the Dolphins hoped he would and was traded this offseason to Tennessee, where he will make $7 million.

The only other questionable one was Long’s and that’s because of injury. He recently took a pay cut but is still expected to be a starter for the Bears.

All the others are either still with their team or have played out their contracts. Only Kuechly and Watt are in the top five of highest-paid players at their positions, which means in most cases the clubs’ early investment kept them from having to work with little or no leverage at the time of signing.

The players, in turn, received huge cash payouts that took the risk out of never making it to free agency because of an injury.

It is necessary to note that only a handful of teams were willing to throw away two years of low-salaried compensation just for the hope an early investment would pay off in the long run.

Among the players who had to wait until after their fourth season to receive extensions were Falcons receiver Julio Jones, Panthers quarterback Cam Newton, Giants receiver Odell Beckham Jr., Raiders end Khalil Mack, Cowboys guard Zack Martin, Rams defensive tackle Aaron Donald, Texans receiver DeAndre Hopkins, Colts quarterback Andrew Luck, Steelers guard David DeCastro and Vikings safety Harrison Smith.

It’s practically a Who’s Who of NFL players.

In the Packers’ case, they must remember that quarterback Aaron Rodgers’ salary-cap numbers get higher every year and the addition of high-priced free agents such as Za’Darius Smith, Preston Smith and Adrian Amos are only going to make their salary cap that much tighter in the years to come.

Getting Clark done now might allow them to offset some of Clark’s future cap costs to this year and next, thereby making his deal more palatable as time goes by. To make that move, you must be confident you’re doing it with the right player at the right time.

The Packers’ priority should be investing in their own players, especially those they know are going to be special. The least they can do is take their best shot with Clark and see if they can hit a home run.