Newcastle lost forward Danny Wicks and delayed decisions on injured duo Jarrod Mullen and Steve Simpson until just before Sunday's crunch clash against Souths at EnergyAustralia Stadium.

Wicks, who has a painful ankle injury which could keep him sidelined for up to a month, will be replaced by Mark Taufua.

Mullen trained on Saturday morning while Simpson sat out the session with coach Brian Smith prepared to give both players extra time because of the importance of the game.

Penalty-magnets Newcastle have done more homework on referee Ben Cummins than on South Sydney in the hope of keeping their slim finals hopes alive.

Newcastle are the most penalised side in the NRL and Smith has looked closely at Cummins' statistics this season in a bid to keep infringements to a minimum against a side which is extremely dangerous with the football.

"We've actually done our homework on the referee Ben Cummins and he's the leading penalty giver in the NRL for players not being square at marker," said Smith.

"We were already on to that (at training) but we practiced again today (Saturday) and made our players very mindful that that referee, by statistical analysis, has a very watchful eye for markers not being square.

"I've got no problem with that as long as it goes both ways.

Skipper Danny Buderus, coming back from injury at a crucial time for the Knights, conceded penalties had been a killer this season and his players needed to be "squeaky clean" against such a dangerous opposition.

"Enough has been said about our penalty rate and stuff but you can't win games like that," said Buderus who heads overseas to play out his career at the end of the season.

"We need to be as squeaky clean as we can on the weekend in that area (penalties) to give us a bit of energy coming down the straight.

"It's up the group and the individual to do his part in the discipline side, whether that's getting back on side or squaring up at marker and the things they have to happen for us to get a fair shot at it."

Smith was concerned at Souths' ability to pile on points if they get enough possession.

"The danger for us is that in the five game winning streak they scored 165 points," he said.

"That's a lot of points and they've got points in them.

"We need to be very good defensively.

"Our number one priority will be to keep the ball and not hand it over through errors and penalties.

"That's the big focus this weekend ... no penalties."

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