Sam Amick

USA TODAY Sports

Right about the time the Golden State Warriors looked unbeatable, even pulling off playoff wins when they had a former MVP on the shelf, there’s this disconcerting development.

Something is wrong with Steve Kerr – again.

The Warriors coach who missed the first half of last season because of a back surgery gone wrong finds himself in yet another fight with his own body, having missed Saturday’s game against the Portland Trail Blazers with what the Warriors ambiguously deemed an “illness." He announced Sunday afternoon that he would miss Monday's Game 4 due to chronic back pain.

He also said he wouldn't return to the sidelines this postseason if his symptoms don't subside.

"This past week, for whatever reason, things got worse," Kerr told reporters on Sunday. "My symptoms got worse, and I was not able to coach. The last few days have been difficult. ... With things getting worse, I just made the decision I couldn't coach. As of now I'm consulting with my doctors, I'm hoping for some improvement. If I can get some improvement, I'll get back on the sidelines. But I'm not going to do that unless I know I can help the team."

It seems his symptoms are related to his previous struggles, that July 2015 debacle in which he had back surgery to alleviate pain only to be subjected to six months of agony when the membrane that surrounds his spinal cord was accidentally nicked. This time around, Kerr’s decision to have lead assistant coach Mike Brown take over his team at such a crucial time speaks volumes about the pain he is known to be experiencing. To be clear, this is not a hospital-bed type situation. Kerr is out and about with his team in Portland, where the Warriors won their second consecutive game without Kevin Durant (calf) in Game 3 on Saturday to stake a 3-0 series lead.

"This is not going to be a case where I'm coaching one night and not the next," Kerr said. "I'm not going to do that to our team and our staff."

On Sunday, when the Warriors had a light practice at the Moda Center, Kerr sat in the stands while players had an optional shooting day and took part in some of the prep work with the coaching staff.

Beyond the bigger-than-basketball part of this, that genuine hope that the 51-year-old Kerr can return to full health and happiness, there’s the reality that this could certainly impact the Warriors’ title hopes. Kerr has been a masterful manager of the Warriors’ loaded roster these past three seasons, leading them to an unreal record of 207-39 in that span (.841 winning percentage) and winning it all in 2015.

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In those deeper rounds, when the Warriors find themselves facing off against coaches like the San Antonio Spurs’ Gregg Popovich or the Houston Rockets’ Mike D’Antoni or a host of other capable coaching minds, the margin for error is razor-thin. It’s one thing to go 39-4 without Kerr like they did with Luke Walton in charge in the first half of the last regular season but quite another to fill that void when the Xs and Os are even more vital in the playoffs.

It certainly helps that Brown, who was hired to last summer to replace Walton when he became the Lakers head coach, is qualified for the task at hand. He spent three years as an assistant under Popovich in San Antonio, where he worked alongside Kerr for two seasons in the later stages of his playing career (they won the title together in 2003). Brown spent five seasons as head coach of the Cleveland Cavaliers during the first LeBron James era (2005 to 2010), then served as head coach of the Los Angeles for the lockout-shortened 2011-12 season before being fired five games into the following campaign.

In all, Brown has a regular season coaching record of 305-187 and a healthy body of work in the postseason (42-29 record) that includes a trip to the NBA Finals in 2007 (the Cavs were swept by the Spurs). What’s more, he has a bona fide sage by his side in defensive guru Ron Adams as well as a respected voice in assistant coach Jarron Collins.

More than likely, they’ll make it work and keep winning games while Kerr recovers. But as long as he is out, that air of invincibility is no more.

Follow USA TODAY Sports' Sam Amick on Twitter @Sam_Amick.