Cooper Cronk was forced to leave Maroons training prematurely on Friday after injuring his ankle.
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The star halfback sustained the injury just 10 minutes into the side's warm-up in the Gold Coast.
Cronk now faces a race against time to be fit for Game I on Wednesday.
New Maroons boss Kev Walters admitted Cronk is in doubt for the clash at ANZ Stadium.
“He’s rolled his ankle... It’s swelled up (like a) pretty big balloon there," Walters said after the session.
“He’s in doubt... I’m not a doctor so I don’t know. Our doctor was pretty optimistic about him playing so we’ll just have to get the scans and see how he comes through that.”
Should Cronk be ruled out of the opener, it is likely Daly Cherry Evans will fill in at number seven.
The Manly half was set to join the Maroons camp on Friday, only for heavy Sydney winds to prevent his flight from taking off.
Cherry Evans' inclusion could serve as a bad omen for the Maroons, who lost game two last year with him starting.
The other replacement option is Michael Morgan, who's addition could see Thurston shift to halfback to accomodate his Cowboys teammate.
If Cronk misses Game I, should Cherry-Evans or Morgan start for Queensland?