Australian halfback Johnathan Thurston is in serious doubt for Friday night's rugby league Centenary Test against New Zealand after rolling his ankle at training.

Thurston is undergoing scans on the injury with Melbourne halfback Cooper Cronk called up to join the squad.

Cronk was to arrive in Sydney on Thursday afternoon and act as cover for Thurston after the North Queensland playmaker went down towards the end of the final training session.

Cronk is the incumbent Australian halfback after partnering Greg Bird in the halves in the Kangaroos' 58-0 win over New Zealand in Wellington last year.

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