He holds the key to Cronulla's NRL premiership hopes but halfback Brett Kimmorley says he won't overplay his hand against title favourites Melbourne on Friday night.

Kimmorley is enjoying the finest form of his 14-year career, leading Cronulla to within 80 minutes of a grand final in his last season at the Sharks.

The former Test and NSW halfback is Cronulla's main attacking engineer, even more so since five-eighth Brett Seymour's unfortunate season-ending knee injury.

Inexperienced 22-year-old Blake Green has been promoted into the starting side for Seymour but Kimmorley said the arrival of the former Parramatta Premier League premiership winner wouldn't force him to alter his game-plan.

"The one good thing we have in our club is that we all know our roles now," said Kimmorley.

"I feel like now I just play footy. I don't run the side anymore which is good.

"I obviously call a lot of things on the field but gone are the days hopefully where I feel like I have to be part of everything.

"I don't think because Blake is there or Buster (Seymour) is not there that I have to step up.

"It might mean we all have to play better this week because it is a bigger game and we've got to be a bit more desperate.

"It is do or die and we probably can't expect the way we played Canberra will beat Melbourne."

Sharks captain Paul Gallen, who remains under an injury cloud with a corked thigh, has little doubt Kimmorley is the key man for his side's title hopes - as long as the forward pack does their job first.

"I think over the past four or five weeks he's been the best player in the competition," said Gallen.

"His experience is second to none, he has won premierships and played at all the big levels.

"The way he is playing at the moment, if our forwards can go forward and control Melbourne's then he can do anything."

Kimmorley won a premiership with the Storm in 1999 and knows Cronulla have a mountainous task trying to beat the most dominant team of the past three years.

Even though the Storm's form has been less dominant recently, with a late loss to the Warriors and last-gasp win over Brisbane, Kimmorley warned Melbourne are dangerous simply because they are truly battle-hardened.

"I think the dangerous part is that after last week they know what do or die is," he said.

"The great thing they did was hang in for the full whole 80 minutes, whereas against the Warriors they didn't.

"It has maybe mentally or preparation-wise touched on a few things they had forgotten about.

"It is just a massive game of football this week and you have to turn up and give it your best shot."

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