Tonga had been named on the team’s extended bench for Sunday’s round 3 clash against the Parramatta Eels.
He made his NRL debut with the club last year, playing in 10 of their 26 games, but has yet to feature this year.
The Dragons have been relatively unscathed in terms of injuries so far, with second-rower Dylan Egan due back from an ACL injury in round 8.
They go into the weekend looking to secure their first win of the season.
They are one of five clubs without a win through two rounds of the competition, and sit 14th on the ladder, ahead of the Brisbane Broncos, North Queensland Cowboys and Gold Coast Titans.
The Manly Warringah Sea Eagles are the other team without a win so far, but they sit above the Dragons because of a superior points differential.