Newcastle legend Adam MacDougall believes Knights star Kalyn Ponga can't lead his side to a premiership from fullback, stating coach Adam O'Brien must move around magnets if he wants to win Sunday's elimination final against South Sydney.

The Knights head into their clash at ANZ Stadium against the Rabbitohs as major outsiders, with Newcastle failing to string together any consistency while Souths trot on from a demolition of the Roosters.

With the Knights tipped for an ugly 80 minutes, MacDougall has warned O'Brien to give the No.1 jumper to someone else in order to get the best out of their star man, Ponga.

“I don’t think you really want your best player being your fullback,” MacDougall told Triple M

“If you look at these great sides - Melbourne, Cameron Smith, they took (him) out of that side a few years ago in a final against the Roosters (and) they got lapped. Billy Slater was still in that side and the best fullback at that time but did he have an impact? Zero.

“The reality is it’s his position that doesn’t really afford him to have the influence on games that he should, because he is a fullback.

“If you’re a first receiver, it’s a lot harder for sides to nullify a first receiver than it is a second receiver, where the defence can aggressively up and in and really target that player.

“They can kick into corners and really give it to him when he runs the ball back and take a lot of petrol out of his tank.

“I don’t really think the Knights should be building their premiership hopes around a fullback. They need to find that X factor in preferably a hooker, which is the one position they are suffering at the moment in.

“If the Knights are going to win this week they need to do something tactically out of the box, and I’d actually be throwing Kalyn Ponga into a first receiver role as a five-eighth.

“You need him with ball in the hands as much as possible.”

League legend Mark Geyer stated that while Ponga's best is damaging, it's not enough to be ranked amongst the league's top tier.

“I think with Kalyn Ponga it seems to me like he needs to find another gear of intensity,” Geyer said.

“When he’s really on there is no stopping him, but when he decides to kick back a bit and be the cool cat he is, he doesn’t get involved anywhere near enough.

“He’s got to find middle ground to join the elite of our game and at the minute you wouldn’t have him in the top 25 players in the game but given his God given talent he should be.

“We should be talking about him like he’s one of our genuine superstars, in the top five NRL players every year.

“I don’t know if that’s because of his status at the club... they can win a comp with him at fullback but at the moment they are long odds.”