Melbourne can't afford another slow start against a desperate Penrith who have labelled Saturday's match their NRL "grand final".

The Storm were forced to claw their way back from 18-0 down in the second half to score a four-point win over Parramatta on Monday night.

While Melbourne are runaway leaders on the competition ladder, the Panthers - ninth-placed heading into round 22 - are desperate to break into the top eight.

"This is a grand final for us this week and that's the way we're approaching it and that's how we'll be playing," Penrith caretaker coach Steve Georgallis said of the AAMI Park match.

"It's a must-win game for us if we're any chance of making the finals."

While the Storm have one hand on the minor premiership, Georgallis - who is set to become an assistant coach at Wests Tigers next season - said his team couldn't survive another loss.

"We can't afford to do that," he said.

"We really need to win this week and we've talked about it as a team and as a group that it is our grand final this week and we must win."

The Storm have eased their players through the short week of training, feeling the affects of their hard-fought victory over the Eels.

The home side are again without two of their attacking weapons in Gareth Widdop and Matt Duffie.

Widdop (elbow injury) and Duffie (sternum) are both expected to return next round.

In his first season as their five-eighth, Englishman Widdop leads the club in line breaks with 14, and is third in the NRL.

He is also second at the club for try assists (12) behind Cooper Cronk and second for tackle breaks (62).

Winger Duffie, meanwhile, is the side's top tryscorer, with 10.

In-form prop Bryan Norrie, who will run out for his 100th NRL match, said they were prepared for another bruising encounter against the Panthers, who haven't won in Melbourne for six years.

"Penrith are a big, physical side and they play good, exciting football," Norrie said.

"We were very happy to win but very disappointed with them (Parramatta) getting a lead of 18 points.

"We were lucky, too. That's not going to happen every week."

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