Already without injured star Will Day (shoulder), and with James Worpel moving to Geelong in the off-season, the Hawks lost young midfielder Cam Mackenzie (concussion) in their pre-season loss to the Western Bulldogs last Friday night.
Newcombe has come under scrutiny over a tackle that drove Ed Richards' head into the ground in the same match.
Richards had one arm pinned by Newcombe but wasn't seriously hurt in the incident, getting up to take his kick and playing out the rest of the game.
But the match review officer (MRO) has the option to elevate the force of an incident based on a tackle's potential to cause serious injury.
The latest MRO findings will be released on Monday.
A grading of medium impact would result in a one-match ban for Newcombe, ruling him out of the GWS clash at Engie Stadium on Saturday night.
The loss of their inspirational skipper would be a blow for the Hawks, who take on an injury-hit Giants outfit first up after last year's preliminary final appearance.
Tom Green (knee), Josh Kelly (hip), Sam Taylor (hamstring) and Toby Bedford (hamstring) are all sidelined for GWS, while Finn Callaghan (hip flexor) still has to prove his fitness.
Essendon are also sweating on Monday's MRO findings, with Sam Durham facing scrutiny over a tackle on St Kilda's Ryan Byrnes.
Durham had one of Byrnes' arms pinned as he picked up his opponent, rotated and took him to ground during Saturday's pre-season match at Ballarat.
If banned, Durham would miss the round-one clash with Hawthorn on March 13.
