Fiji fly-half Caleb Muntz, who scored 15 points in the historic test win over England last month, has been ruled out of the Rugby World Cup due to a knee injury, said coach Simon Raiwalui.

Raiwalui added it was "devastating" for the 23-year-old and the squad, coming just days before their opening Pool B game with Wales in Bordeaux.

Muntz, who only made his test debut in July against Tonga, suffered the injury during the team's training run on Monday.

"It's most devastating for us as a group and for Caleb," said Raiwalui.

"He has worked so hard for the past two years with the Fijian Drua (Super Rugby franchise) and for Flying Fijians.

"We feel for him as a young man that he misses the opportunity so close to the Rugby World Cup."

Raiwalui said they were considering who to bring in to the squad to replace Muntz but added he had confidence in his other fly-half Teti Tela.

Tela, 32, also plays for the Drua.

"We have got 33 players and we have the utmost confidence in them," said Raiwalui.

"Once we name the team for the match against Wales we will have utmost faith in whom we have selected."

Fiji enter the tournament with live hopes of reaching the quarterfinals for the third time after previously making the last eight in 1987 and 2007.

Aside from them and Wales, whose recent form has been patchy, Pool C also includes Australia, yet to win a test this year, Georgia and minnows Portugal.