Most Important Free Agent for San Antonio Spurs to Land If Tim Duncan Retires

For what seems like an eternity, Tim Duncan has been the cornerstone of the San Antonio Spurs. Sooner or later, however, the five-time NBA champion will be calling it a career.

While that statement has become a yearly event, once again, the 18-year veteran's NBA future is uncertain.

According to Sam Amick of USA Today, San Antonio coach Gregg Popovich said, "If you ask me, my guess is that [Duncan will] go for another one because he has been so consistent this season."

Yet if Duncan indeed retires following the 2015 campaign, the Spurs must be ready to replace their legendary power forward with an established talent.

According to Sean Deveney of Sporting News and Zach Lowe of Grantland, San Antonio has already been tied to Marc Gasol and LaMarcus Aldridge respectively, but neither player is a very realistic option because both are likely to return to their current team.

Greg Monroe, on the other hand, would be the most important free agent for the Spurs to pursue and potentially land.

A 6'11", 253-pound power forward for the Detroit Pistons, Monroe has tallied 16.0 points and 10.4 rebounds this season, shooting 49.6 percent from the floor and 74.3 from the free-throw line.

Although he'll likely leave the Motor City this summer, the former first-round pick said he's not worried about what will happen, since he must continue to work back from a knee injury right now.

"I'm just trying to finish the season," Monroe said, per Vince Ellis of the Detroit Free Press. "That's about it. I still haven't thought about that yet. I've just been focused on doing everything I do to get my knee back."

Monroe will be an unrestricted free agent once the calendar reaches July 1, and the Georgetown product figures to have suitors in the Los Angeles Lakers, Boston Celtics and New York Knicks, to name a few.

What's more, according to Steve Kyler of Basketball Insiders, "the Spurs were...believed to be the team with the most interest in Monroe last summer." So, if Duncan retires, it's safe to assume San Antonio should again check on Monroe. But this time, with a little more intensity.

The Spurs cannot offer a starring role like a rebuilding roster does, but according to Ellis, Monroe's agent David Falk is making sure his client is considering every aspect. He said:

"

He's going to get the same money wherever he goes. I told him that two years ago. All stars get the same amount. It just depends on what the intangibles are.

Where do you want to move? Who do you want to play with? Who do you want to play with? Is there a coach you want to play for? Do you want to be the star on a rebuilding team or do you want to be a complementary player on a championship team? Those are all intangibles.

"

A tender 25 years old at the beginning of the 2015-16 season, Monroe offers tremendous offensive value near the basket. He's converted on 44.1 percent of his post-ups, per NBA.com, a notable increase on Duncan's 39.4 mark.

Additionally, Monroe has buried 49.5 percent of his attempts as the roll man compared to Duncan's 48.4, though admittedly in a smaller sample because the Pistons' offensive system typically doesn't utilize Monroe that way.

But mediocre shooting range—his most glaring weakness—is a key reason Monroe is more of a complementary player rather than a superstar. The lefty has only attempted 13.5 percent of his career field-goal attempts from beyond 10 feet. 

While Duncan has slowly dropped the mid-range jumper from his repertoire, San Antonio must be aware of the potential lack of spacing if Monroe logged significant minutes alongside Tiago Splitter.

However, they'd balance each other defensively, considering Splitter's strength of rim protection can atone for Monroe's issues as a shot-blocker.

Plus, according to Basketball-Reference.com, Monroe has posted a 25.6 percent defensive rebounding clip—comparable to Duncan's 26.5—in a frontcourt shared with glass-eater Andre Drummond.

Monroe's numbers would likely soar as a part of the defensive-oriented Spurs, while he'd immediately become the premier weapon on the offensive boards.

With all that being said, the fifth-year pro's prospective future in San Antonio could hinge on the decision of a shooting guard.

Paul Sancya/Associated Press

Per HoopsHype salary figures, this offseason, the Spurs will have approximately $33 million of cap space, though there's $48 million before the luxury tax line. San Antonio will presumably re-sign Kawhi Leonard to a max contract, eliminating about $15 million.

The front office would still need to add seven or eight more players with the remaining money, and Danny Green needs a new deal. The three-and-D asset will likely command a high-seven, low-eight-figure contract in free agency.

So, the Spurs could be forced to decide between Green and Monroe, because the franchise's financial outlook is certainly tight.

But if the soon-to-be 39-year-old Duncan calls it a career, a pure post man in Monroe could take priority over a sharphooter, something San Antonio has replaced many times before. Granted, it might take a shrewd bit of cap manipulation, and Monroe must be willing to remain a complement rather than the main event.

But no matter what eventually happens, the Spurs would be wrong not to chase the best, most available free-agent post player on the market. Landing Monroe if Duncan retires would help the Spurs remain one of the top franchises in the league.

Unless otherwise noted, stats are courtesy of Basketball-Reference and are accurate as of April 6.

Follow Bleacher Report NBA writer David Kenyon on Twitter: @Kenyon19_BR.