Manu was carted off the field near the end of the first half and coach Jamie Joseph said after the game it appeared as though Manu has either broken his foot or his ankle.
''It is a real shame for Nasi as he has been training really well and got himself in top condition,'' Joseph said.
He was heading to the hospital after the game for an X-ray.
Manu had enjoyed a productive first half and was carting the ball up well, making the advantage line. He has been a rock for the franchise over the past couple of years, having played every game in 2011 and missing just one last year.
With Manu off the field and Adam Thomson on his way to a club side in Japan, the Highlanders loose forward trio had a different look to it last night.
Manu was replaced by Elliot Dixon, who was busy in the second half but is still inexperienced at this level.
Joseph said injuries had struck hard for his team already.
Another No 8 option, Jake Paringatai, would play a game for the Highlanders development side in Christchurch today after not playing any pre-season due to a broken handThe side had a bye next week and although it was early in the competition, with the amount of injuries the team had it was coming at the right time, Joseph said.
The Highlanders' next game is against the Cheetahs in Invercargill on March 9.