Kalyn Ponga could return to play sooner than expected after breaking his arm in New Zealand's 24-22 loss to Australia, former Australia halfback Brett Kimmorley said.
Kimmorley noted that Jahrome Hughes and Blayke Brailey resumed playing three weeks after arm fractures. Ponga had surgery on Friday night and remains with New Zealand's squad.
New Zealand are technically carrying one fewer player if Ponga cannot play, Kimmorley said, but will give him time to recover.
Tonga began their campaign with a 30-12 victory over England in Perth and face Lebanon in Sydney on Friday.
Kimmorley expected Tonga to win and said the result put them among the World Cup's leading contenders.
He praised halfback Isaiya Katoa's kicking and playmaking. Katoa made seven of eight conversions and penalties despite not usually handling goal-kicking for the Dolphins.
"Kicking game was first-class, ball-playing, just has got so much time and players like running off him and creates opportunities and that will be very, very dangerous in this tournament."
Kimmorley also highlighted Roosters centre Robert Toia and Tonga captain Jason Taumalolo, whom he credited with inspiring Pacific players to represent their heritage nations.