Gavet will have surgery this afternoon on a ruptured anterior cruciate ligament (ACL) that requires a full knee reconstruction.
The incident happened last Thursday morning when he stepped awkwardly at the Broncos’ final training run before the Friday match against the Cowboys.
Gavet was running defence against the NRL team as he served week two of a three-week sentence incurred in round one.
It is an unkind blow for the 25-year-old, who had worked hard in the off-season after being recruited from the Tigers last year.
He will now begin a recovery that generally takes six to nine months and gives him little chance of playing again before the season is out.