Surgery is not thought to be an option; his problem is degenerative. His knee is living proof that, when a movable object spends a decade hitting irresistible force, the latter comes off best.
This uncertainty casts doubt on what path his future career will take as he's off contract this year. All Black coach Steve Hansen picked Williams last year after the big lock chased shadows from February to June. It would be a little cruel and unjust to not pick Williams now that he's deserving a spot.
Williams, should he maintain his form, will almost certainly be selected by the All Blacks. Here's where the vicious cycle begins, though. To maintain his form, Williams has to play and the more he plays, the greater stress he puts on his knee.
The All Blacks might wonder what Williams will have left by June - only Richie McCaw is good enough to get away with playing on one leg. His best option is smart management between now and the French series.
He's resisted so far. He's revelling in the captaincy, feels an obligation to be an 80-minute man and go the distance with the troops.
Admirable, but not particularly wise in terms of helping his longevity. The Hurricanes game last week was a classic case where he could have left the fray early - the game was over after 65 minutes.
There is little doubt that, if he can make the All Black squad, then he'll sign on for more next year.
"We certainly want to keep him," says Blues coach John Kirwan.
At 31, Williams knows this will be his last chance to cash in offshore, should that be his fancy. But, with multiple business interests in New Zealand and the lure of being the man to lead the Blues to the better future they appear capable of now enjoying, the prospect of foreign riches doesn't hold much appeal.
Everything comes back to that knee of his. He won't be an All Black if he can't run. He won't be able to captain the Blues if he can't jump or get around the track.
The Blues are doing what they can to build their locking stocks for next year. They will be losing Anthony Boric who is off to Japan and they know that if they have another big man in the mix, a tight, grinding, bruising lock, then they can manage Williams' workload next year.
They need him on the field. They want him on the field but not for every minute of every game.
"It's hard to find big men, though," says Kirwan. "We are looking and talking to people but most of the established guys are already contracted."