Glenn Phillips could be in line for a shock test debut after being called into the Black Caps as last-minute cover.

The Auckland batsman is flying to Sydney tonight to link up with the Black Caps, after illness swept through the team ahead of their third and final test against Australia at the Sydney Cricket Ground.

Captain Kane Williamson, batsman Henry Nicholls and all-rounder Mitchell Santner are all suffering from flu-like symptoms, with Williamson and Nicholls missing the last two trainings due to viral infections, and Santner also being quarantined in the hotel after feeling unwell this morning.

Williamson is tipped to play unless his condition worsens overnight, but there is more doubt over Nicholls, with Phillips' call-up a potential indicator that at least one of them may not be fit come tomorrow morning.

It also potentially suggests a lack of faith in dropped opener Jeet Raval, with Phillips arguably a better choice to jump straight into the starting XI if required, having been in solid form recently, and offering far more versatility - being able to bat in multiple positions.

Phillips, who also keeps wicket, averages 42.6 in first-class cricket, and has had several standout moments this season. He averages 72 in the one-day competition, having blasted 156 against Otago, and hit an unbeaten 106 in a Twenty20 match against the same opposition.

The 23-year-old's last first-class game was also promising, scoring 116 for New Zealand A against England in November.

Phillips, who has played 11 Twenty20 internationals without much success, could potentially make it four wicketkeepers in the Black Caps' starting XI tomorrow, alongside Tom Latham, Tom Blundell, and designated test gloveman BJ Watling.

Black Caps coach Gary Stead stressed Phillips' inclusion was precautionary, and is still hopeful that Williamson and Nicholls will be fit to play.

"It's a bit of an unknown how they're going to recover," Stead said.

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"We've obviously got a few balls up in the air at the moment and we want to be on the safe side and have options.

"Glenn has been in terrific form this season and has good versatility with where he can bat and the roles he can play. He's been around the Black Caps T20 team for the past couple of years so should feel comfortable in the environment.

"We're still hopeful Henry and Kane will pull through and we will give them every chance to prove their fitness. If one or both are ruled out then we will consider our options and most importantly how they balance the side for this final test."

But, if required, Stead believes Phillips is an excellent - and versatile - option for the Black Caps to call upon.

"Glenn covers everywhere from one down to five or six for us. He plays pace and spin really well, and he's lightning quick between the wickets.

"Whilst he hasn't had experience at this level yet, we think further down the track there's that potential, and who knows, it could even be tomorrow."