Wigan have confirmed scrum-half Thomas will be sidelined for around two months after he broke a leg in the Exiles' 18-10 defeat by England on Saturday.
Leuluai, who captained the Super League-based overseas side, was carried off on a stretcher in the second half at Langtree Park after twisting awkwardly and went for scans yesterday which revealed the break as well as ankle-ligament damage.
Wigan coach Shaun Wane expects his player to be out for six to 10 weeks but insists he will be back before the end of the season.
"It is a blow for Tommy and for the club," Wane said.
"But the results of the scan are a lot better than I expected. He will play again this year.
"The injury is a clean break whick will mean a couple of months on the sidelines and we look forward to his return to the side at the business end of the season."
Leuluai, who is leaving the club at the end of the season to rejoin New Zealand Warriors, will miss his side's Challenge Cup semi-final against Leeds on July 14 and could be a doubt for the August 25 final if the Warriors reach Wembley.
Leuluai has missed only one game so far this year but at least Wigan will have his half-back partner Brett Finch available for their next Super League game, at home to Widnes next Monday.
Finch and centre George Carmont both pulled out of the Exiles squad with minor knocks sustained in the Warriors' 36-14 win over Catalan Dragons nine days ago.
"Brett needed a rest," said Wane.
"He took a slight knock against Catalans and George has had a tough season and also needed a break."
Wane is likely to switch Finch to scrum-half and move captain Sean O'Loughlin from loose forward to stand-off in the short term.
Long term, the club are thought to have signed Salford's Matty Smith as a replacement for Leuluai and lined up a big money offer to Castleford for Man of Steel Rangi Chase.