Manly star Brett Stewart is to undergo surgery next week on his left knee and will be sidelined for up to five months of the NRL season.

Stewart received the shattering news late on Tuesday night and coach Des Hasler revealed the extent of the injury at club training on Wednesday.

The injury is identical to the one he sustained on his right knee last season which sidelined him from round five until round 25.

Stewart suffered the injury when making a try-saving tackle on Wests Tigers winger Lote Tuqiri late in Monday night's match at the Sydney Football Stadium.

"It is a shattering blow to Brett personally and to us as a club but we have to be positive and he is being positive despite his recent run of bad luck," said Hasler.

"We proved we can win matches without him last season and we can do it again.

"It's not the end of the world by any means but it would be ridiculous not to suggest he won't be missed. He is a champion player."

Stewart has told teammates he will be back on the field with them inside five months.

"He has set himself round 20 and it is good he is setting himself goals," said Sea Eagles chief executive Graham Lowe.

"The Manly club knows how much of a fighter Brett is and he will be given the best of medical and rehabilitation support to get himself back where he belongs as soon as possible.

"He has been through it before and knows what to expect."

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