''We're just working through that knee," New Zealand batting coach Craig McMillan said today.
''It's just a little bit niggly so we want to make sure it's a hundred per cent.
''We'll see how he feels (on Christmas Day) and make a decision.
''We need to get it right, if a little bit of a break will help it that's something we'll consider," McMillan added.
Williamson spent time with medical staff as teammates, including debutant-in-waiting Henry Nicholls, started their training session in Christchurch today with a football game.
Meanwhile Sri Lanka's ambitions in the ODI and T20 series have been hit by the withdrawal of star fast bowler Lasith Malinga.
It was always doubtful whether Malinga would make the start of the limited-overs section of Sri Lanka's tour as he battled a knee injury.
However having him ruled out of the entire trip is a heavy blow for a squad already without the experienced Dhammika Prasad.
Malinga, who has 291 wickets in 191 ODIs with his round arm slingshot action, has stayed back in Sri Lanka for rehabilitation on an injury he picked up against the West Indies recently.
The 32 year-old, who retired from test cricket in 2011, has been replaced in Sri Lanka's squad by big hitting allrounder Thisara Perera.
''That's a big loss, what a contributor he's been over a number of years for Sri Lanka," McMillan said of Malinga.
''He's been their key fast bowler.
''He's a handful. I'm sure they'll miss him, but it gives an opportunity to some other younger guys in the squad," McMillan said, referring to Dushmantha Chameera's growth during the two-test series. The young speedster, who starred with nine wickets in the Hamilton test, is also in Sri Lanka's limited-overs group.