This marks the second time Mike Krzyzewski has left his team in midseason. The first occurred in 1995 and has since been ascribed to pain and exhaustion. (He'd had back surgery four months earlier.) The sport's best coach basically dropped out of sight for 2 1/2 months, and nobody knew if he'd return. Spoiler alert: He did.

This time he's leaving to have surgery to repair a herniated disc. The time of recovery is estimated at four weeks. That's only an estimate, and backs are notoriously tricky things. The sport's best coach -- among the greatest in any sport ever -- has a team good enough to win the NCAA championship, which would be his sixth and bring him within four of John Wooden. But Duke's title chances will slip if Jeff Capel is in charge come March.

That's no knock on Capel. It's just that there's only one Krzyzewski, and he's about to have back surgery, and -- this is no small point -- he'll turn 70 on Feb. 13. The aforementioned Wizard of Westwood retired at 64. Dean Smith stepped aside at 66. Adolph Rupp was shoved into retirement at 70.

Nobody at Duke will push Coach K to do anything he doesn't want to do, seeing as how he essentially runs the school. (And sometimes the ACC if not the whole wide world, if we credit the conspiracy theorists.) Still: He's turning 70. Steve Spurrier insisted he'd coach several more years; he kept insisting until he quit in midseason at 70.

The point being: No matter how healthy the sport's greatest coach appears to be, and no matter how adept he is at delegating, the days of K at Duke are nearing an end. This back surgery could rejuvenate him in a way that makes him feel he can go on forever -- remember, this is the guy who was coaching the nation's flagship program while also guiding the U.S. men's Olympic team the past 10 years -- but nobody goes on forever. It's hard to imagine him (or anyone) coaching Division I college basketball at, say, 75.

It was intriguing that his second-to-last act before taking his medical leave -- the last was beating Georgia Tech by 53 points at Cameron on Wednesday -- was to reinstate serial tripper Grayson Allen . The "indefinite" suspension lasted one game. (Duke lost at Virginia Tech, not incidentally.) Not many coaches could get away with that, but no other coach is Mike Krzyzewski, who does as he pleases.

Coach K's defenders will say he made the decision to spare Capel having to do it and face the inevitable fallout. Still, this seemed an act of hubris. A guy trips three opponents in 10 months before getting suspended for anything, and when finally he does it's for one game?

This prompted another I-know-better-than-you lecture from Krzyzewski, who usually does know better than we do. It also reminded us that he's still Coach K, the greatest basketball coach since Wooden and maybe the greatest ever. He may be pushing 70 and facing yet another round of back surgery, but he still does as he pleases.