Amone's case was back before Wollongong Court on Wednesday, after being charged in December in relation to an alleged attack on a roofing contractor.
The NRL subsequently announced the 20-year-old five-eighth would be stood down under the game's no-fault stand-down policy, as he fights a charge of causing reckless grievous bodily harm in company.
Amone faces a maximum 14 years in jail if found guilty of the offence, above the NRL's threshold of 11 years for the stand-down policy to be automatically enacted.
"The NRL has advised the St George Illawarra Dragons that Talatau Junior Amone is subject to the mandatory no-fault stand-down condition under the NRL rules," the league said in a statement.
"Under the condition, the player is not permitted to participate as a player in the NRL competition or any related, representative or other competition or pre-season trial match."
Amone had been training with the Dragons since returning from last year's end-of-season World Cup.
Whether he continues to do so rests with the Dragons and Amone, as the club gathers further information on how long the court proceedings will likely last.
Sullivan was expected to be the man who could step up as the Dragons' No.6, however he has now been hit by injury.
The 21-year-old is expected to be sidelined for four-to-six weeks with his hamstring problem, ruling him out of the pre-season clash with English club St Helens.
He is an outside chance for the Charity Shield clash against South Sydney on February 18, with the club hopeful he can be fit to face Gold Coast in the Dragons' season opener on March 12.
Time in the trials alongside halfback Ben Hunt would have been crucial for Sullivan, with the pair having not partnered each other in the NRL since two games in late 2021.
If Sullivan is not fit, coach Anthony Griffin would likely have to hand the No.6 jersey to versatile Moses Mbye to start the year.
Sullivan's injury leaves the Dragons with a second spot in their spine in question before kickoff.
Fullback Cody Ramsey is sidelined by serious illness, with no certainty on his return date.
Tyrell Sloan is the likely back up No.1, after he started last year there before being dropped midway through the season.
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