Cronulla coach Shane Flanagan believes Sunday's clash with South Sydney is his side's most important game of their NRL season.

The improving Sharks have won their last two games, but they must do battle against an injury and suspension-hit Souths side without their talismanic skipper Paul Gallen, who is on State of Origin duty with NSW.

Flanagan said the Sharks need to prove they are not a one-man team, and that victory over Souths could be a season-defining result as they get the rare opportunity to play in front of their long-suffering fans on a Sunday afternoon.

"I have been really pleased with how we have played in our last two games, we had to beat a Canterbury side desperate for a win and then up against a Gold Coast side, who although they are struggling, are still hard to beat at home," Flanagan told AAP.

"We are still a long way from where we want to be, but I think if we can beat Souths then we would have turned a corner in our season.

"Our problem has been in the past, not being able to follow one good performance with another, but we have now done that and the mood among the players is fantastic and for once we have no major injury concerns."

Explosive fullback Nathan Gardner has been in fine form, scoring three tries in as many games, and Flanagan has been delighted with the way he has bounced back from an ankle problem that sidelined him for six weeks.

"We have been really happy with him, he gives us a real cutting edge and is getting better and better with each game," he said.

"He is still only 21, learning the game, but there is more to come, he has a big future ahead of him."

In the absence of Gallen, Flanagan pinpointed his powerful forward pack as being the key to overcoming a Souths side missing Sam Burgess, Roy Asotasi and the suspended David Taylor.

"Jeremy Smith's return has been vital in our last two wins and Luke Douglas, Kade Snowden and Jayson Bukuya have been really strong for us," he said.

"Jayson has had to overcome serious shoulder and knee injuries over the last two years and the fact he's playing so well shows what great character he possesses.

"This is the chance to give our fans something to cheer about and without doubt this is our biggest game of the year as it can hopefully give us a platform to move up the ladder."

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