Tonga withdrew from the Oceania Championship three months ago after the team was quarantined for measles but were thrown a lifeline after World Rugby agreed to a revised qualification process.
Fiji has already secured their spot after beating Samoa 41-13 in the Oceania qualifying final, with the winner of this weekend's match in Port Moresby to playoff against the Manusina in April for a place in the final World Cup repechage tournament.