Sculthorpe had been playing with the aid of a cortisone injection.

Sculthorpe was to undergo surgery on a persistent knee problem at the end of the domestic season but has brought forward the operation to Monday.

The versatile 29-year-old will also miss the start of next season.

The Great Britain captain said: "It'd be unfair to my team-mates to continue at this crucial stage of the season."

Sculthorpe has been plagued by knee problems over the past two years and had recently been playing with the aid of a cortisone injection.

Although the operation will cause him to miss the start of next season, we expect him to come back much stronger Saints coach Daniel Anderson

He was already due to miss the Tri-Nations Series for a second successive year after agreeing to an operation after the conclusion of the domestic season.

"I have been playing on, hoping that I would be able to reach the high standards that I have set myself throughout my career," he added.

"However, I have not been able to do that.

"The club has been very supportive, and I am planning on repaying their patience when I return to action next season."

Sculthorpe, restricted to just 20 appearances this season, led Saints to Challenge Cup glory in August.

But his six-month absence will be a major blow for Saints, who face Hull for a place in the Grand Final at Knowsley Road on Friday.

Coach Daniel Anderson said: "Paul is a first-class captain and consummate professional, which is why he has taken this courageous decision.