Cronulla on Tuesday confirmed the worst possible news for their star halfback, who will miss approximately eight weeks with the injury.
Hynes went down at Sharks training on Monday, and was helped off the park by two men before being sent for scans.
The 2022 Dally M Medallist has seen specialists since then, and is now unlikely to return until at least the eve of the finals.
"It has been confirmed that Nicho has a complete syndesmosis rupture, plus a tibia fracture to his left ankle," Sharks performance boss Nathan Pickworth said.
"He will undergo surgery tomorrow (Wednesday), with an estimated return to the field of approximately eight weeks."
The injury comes as a massive blow to the Sharks, who have lost five of their past six games to fall from first to fourth on the ladder.
Sitting pretty for the minor premiership two months ago, Cronulla are now only four points clear of 10th-placed St George Illawarra.
Dan Atkinson will come into the halves in place of Hynes, and will partner Braydon Trindall.
Forward Jack Williams is also expected to miss Friday's clash with Wests Tigers with a wrist injury.
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