Waisake Naholo an injury worry for New Zealand's Rugby World Cup title defence

The Otago Highlanders player suffered the setback in training

Waisake Naholo, centre, is a doubt for the Rugby World Cup due to a knee injury. Getty

New Zealand winger Waisake Naholo's hopes of making the Rugby World Cup in Japan later this year hang in balance after he suffered a knee injury at training that ruled him out for up to six weeks.

The 27-year-old, a member of the All Blacks World Cup winning-squad in 2015, had a scan on Tuesday and was diagnosed with "a grade two MCL injury", the Otago Highlanders said in a statement.

"He is currently in a knee brace and will be unavailable for up to six weeks while he is rehabilitating," the team added.

The injury could not have come at a worse time for the Fiji-born Naholo, who has appeared short on confidence and has not played at the level that earned him 26 caps for the All Blacks.

His expected return in mid-May would give him just four regular season games to convince All Blacks coach Steve Hansen that he would be able to regain his form ahead of the Rugby Championship and force his way into World Cup contention.

New Zealand have won the past two tournaments and will begin as favourites to claim a third one on the trot when the tournament gets underway in Japan in September.

Their opening match is against South Africa on September 21 in Yokohama and they will also go up against Italy, Namibia and Canada in their Group B fixtures.

Naholo is one of several All Blacks battling long-term injuries ahead of the tournament.

His Highlanders teammate Liam Squire also suffered a knee injury at training last month, while Sam Cane is still recovering from a broken neck he sustained last year.

Captain Kieran Read, who came back game from an extended break on Friday, was also an injury scare for Hansen as he had to be replaced after 40 minutes due to bruising to his right leg against the Wellington Hurricanes.

Naholo will be sorely missed by the Highlanders, who have lost three of their last four games and not won since week two of the competition, dropping to fourth in the New Zealand conference.

Their match with the Canterbury Crusaders three weeks ago was cancelled due to the shooting at two Christchurch mosques on March 15 that killed 50 people.

The Highlanders will face the Hurricanes in Dunedin on Friday before travelling to Christchurch for the return game against the table-topping Crusaders on April 12.