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The Golden State Warriors have multiple concerns after falling to the Houston Rockets in Tuesday's season opener. Head coach Steve Kerr is unhappy with his team's physical and mental conditioning, and a number of key players are nursing injuries. 2015 Finals MVP Andre Iguodala has a sore back, while newcomer Omri Casspi is dealing with tweaks to both of his ankles.

More importantly for the Warriors, All-Star forward Draymond Green went down with a left knee strain in the fourth quarter of Tuesday's game. "I don't think it's serious, but we'll see," Kerr said Wednesday afternoon. Per ESPN's Chris Haynes, Green's MRI came back negative. Mark Medina of the Mercury News has him listed as probable for Friday's game in New Orleans.

The prospect of a prolonged absence for Green, who anchored the Warriors defense during their 16-1 run to last season's championship, should give team officials pause. Despite the roster's evident depth, the array of skills and intangibles the former Michigan State Spartan brings to the table simply cannot be replicated with the Warriors' current personnel.

It all begins with Draymond's mental conditioning. Of his team's collapse during the 2016 NBA Finals—in which the Warriors memorably blew a 3-1 lead over the Cleveland Cavaliers—he readily admits having not taken the backlash from his groin-smacking, suspension-eliciting roadshow in stride. But since that time, he has taken advice from competitive sage Kobe Bryant to heart. Per Clay Skipper of GQ, the Black Mamba told Green, "As long as you wait for them to understand you, you're f--ked."

Draymond isn't trying to be understood anymore. He's actively coaching himself not to care, and his increased mental fortitude contributed to his team's success last season.

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He may not care about your opinions or mine, but he'll definitely tell you what he thinks. He'll tell you again and again, with nuance, or profanity, or both, depending on his mood. He doesn't hold back.

"A closed mouth doesn't get fed," says Warriors assistant coach Jarron Collins. "Draymond's a big believer in that philosophy."

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Off the court, Draymond says what he wants, and he doesn't suffer fools. On the hardwood, he brings the Warriors what their pre-championship era longed for on a game-by-game basis: a player you'd love to hate if he were on another team. An enforcer.

"Playing against him, he was always vocal," says Casspi about his first impression of the trash-talking forward. "But when you get a chance to see him on a day-to-day basis you see how great of a competitor he is; how much he understands the game."

Draymond is one of the most cerebral enforcers the NBA has seen. Prior to injuring his left knee in Tuesday's 122-121 loss to the visiting Houston Rockets, Green was his usual stat-stuffing self, putting up 13 assists and 11 rebounds to go along with nine points. Though he wasn't quite as impactful on the defensive end (he fought early foul trouble), had he been able to finish the game, his presence could have been the difference for the Warriors.

Quietly, Draymond has become his team's most important player.

In vindicating his loss of control during the 2016 playoffs by leading the Warriors through a dominant run to the 2016-17 title, Draymond demonstrated his knowledge of the game, as well as his worth to his team. The forward—generously listed at 6'7"—paced the Dubs in rebounding and stocks (steals plus blocks), and managed to shoot the lights out from three (.410) while taking fewer than 10 shots per contest. His playoffs-long box score line of 13.1/9.1/6.5 is certainly formidable, though it does little to demonstrate the full scope of his impact.

The Warriors cut through the field behind the potent scoring of Stephen Curry and Kevin Durant, but it was Draymond holding down the back line that fueled their downhill attack. Green led the team in defensive win shares and posted some of the more demoralizing defensive stops the 2017 playoffs had to offer, all while dropping dimes at a Curry-esque clip.

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Despite his achievements—two NBA championships, two trips to the All-Star Game and the 2016-17 Defensive Player of the Year award—Green still has detractors. Around the national water cooler, the mercurial Michigander's game does not always glitter alongside the sheen of his gilded environment. Just recently, former Warriors teammate and playoff foe Richard Jefferson went so far as to say Green is in a "fully supporting role" with the Warriors. The implication is that Draymond's skill set is replaceable, or even that the Warriors could win it all without him.

Well, they just can't. In the same way that Curry is the Warriors system, Green is their backup system. He is the spinach inside Popeye's aluminum can. He's the auxiliary power on the Enterprise. He's the vodka filling James Bond's martini glass.

For starters, in a sense wholly unlike his trio of All-Star teammates, Green is a statistical marvel. During a 15-point win against the Grizzlies last February, he came within six points of recording a quadruple-double (and one point from recording the elusive "five by five"), with 12 rebounds, 10 assists, 10 steals and five blocks. It was the first triple-double ever recorded in the NBA without at least 10 points.

(The Warriors are undefeated in the regular season (19-0) when Green registers double digits in three of the five basic statistical categories.)

Anchoring the NBA's second-stingiest defense in 2016-17 (including ample garbage time), Draymond led the Association in defensive box plus/minus and was within percentage points of leading the league in defensive win shares, defensive rating and stocks. The man sees things happening on the court before they happen, and somehow occasionally manages to guard the entire opposition.

"[Draymond] is probably one of the sharpest basketball minds I've been around," says Collins. "He understands his opponents, what they want to do to be successful. He understands angles, leverage, technique—he just has a great feel for the game."

That feel is not limited to getting stops. Astoundingly, Draymond—not Curry—led the Warriors in assists per game last season, recording more helpers than any forward in the NBA not named LeBron. Within head coach Steve Kerr's pace-based system, Green often pushes the Dubs offense downhill, initiating the break after a defensive rebound or functioning as a safety valve in the backcourt when Curry is double-teamed. Green's preternatural eye and ambidextrous passing touch make him especially dangerous in triple threat, as well as on the run.

Add in the fact that Green has forged a strong bond with Durant, and one begins to see how integral he is to the the Warriors' success.

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Yes, Durant is clearly the better player. Curry, too. And Klay Thompson is by far the more polished scorer despite being tasked with hounding All-Star wings night in and night out. The three superstars combined for 73 of Golden State's 116 points per game last season. That's potent stuff.

Behind them is Zaza Pachulia and JaVale McGee, who provide the necessary bulk for the Warriors to play big. With new additions Casspi and Nick Young playing positionless basketball alongside Andre Iguodala and Shaun Livingston, the Warriors look to be deeper than ever.

But what happens to them without No. 23? Where is the backup's backup?

The Warriors brought on KD as the ultimate insurance for an injury to Curry. Engine busted? Just replace it. Not exactly light-years ahead, but smart.

However, there's no such thing as Draymond insurance. The Warriors' success hinges on his health.

Green doesn't often sit out games, though. Last season, his age-26 campaign, was his least healthy—he missed six contests in all.

Even in the event of an injury, you can bet Draymond would still be looking for ways to back up his squad. He has spoken at length about taking rookie Jordan Bell under his wing, training Bell in the skills and intangibles that give the two-time All-Star his edge.

"It's a great thing to have, somebody you look up to, him being one of my favorite players [growing up]," says Bell, who got more acquainted with Draymond during the Warriors' week-long trip to China in early October. "I mean, he's not always yelling like everybody thinks he is. He talks a lot, so he knows when to turn it on and off."

In Casspi's equally short time as a Warrior, he has also observed the qualities of leadership in Draymond. "Sometimes he'll be the one that stops practice if he sees something. He's earned that respect with the coaches and the guys here because he picks all the right spots."

So, Draymond is an energized vocal leader who has made himself utterly indispensable to a team full of stars. He's a coach on the floor and a mentor off of it. He's the league's best, most versatile defender. He's a point forward who's a constant threat to record a triple-double, and he does it all while necessarily being the guy everybody loves to hate.

Talk about value.

What would the Warriors be without Draymond Green? Aside from much less interesting, they wouldn't be the reigning NBA champions. If they aim to repeat, they absolutely need him.

Aliko Carter covers the Golden State Warriors for Bleacher Report. Follow him on Twitter @kogitare. All quotes obtained firsthand unless otherwise noted.