Manly five-eighth Cade Cust left the field on Sunday limping from two separate leg injuries but with teammates crowding the club's casualty ward, he is determined to soldier on.

In the eighth minute against the Knights in Newcastle, he hurt his left knee – five minutes after scoring the opening try – and in the second half he rolled his right ankle.

"I'll be fine for next week," he told NRL.com, while walking surprisingly freely after playing 72 minutes injured in the 26-24 loss.

And Manly will need him as they face a confidence-filled Rabbitohs outfit at ANZ Stadium on Saturday bouncing along for their fourth win in a row.

With fullback Brendan Elliot already gone for the season due to a torn ACL, Manly were desperate for Cust to stay put in a reshuffled backline – and he did.

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"Just the will to win," Cust said, when asked how he managed to play on.

"We really wanted to win that game. It hurt a lot really – the game, not my legs – because we had a few chances to win and the two points got away from us there at the end.

"I just got a few niggles but they're alright. I looked after them after the game and I'll do the same all this week."

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Cust said the thought of coming off never crossed his mind even though bench utility Lachlan Croker could have filled in at five-eighth.

The 21-year-old played the second half with his left knee heavily strapped.

Coach Des Hasler said Cust's performance was "inspiring" but he left it at that. Hasler expects all his players to do their job no matter what number is on their jersey, or the pain in their body.

He has scored three tries and two try assists in his seven games in place of regular five-eighth Dylan Walker, who is having a season of mostly rehabilitation with two foot injuries restricting him to only seven appearances in 14 matches.

Cust's presence has made for a seamless transition in the halves. And if he keeps pulling off tries brimming with instinct and skill like he did against the Knights, Walker can take his time in getting his foot right.

After being on the spot for Brad Parker to bat back a Daly Cherry-Evans bomb, Cust skimmed the sideline then threaded a kick through two pairs of Knights legs before chasing it into the in-goal area and winning the race with Gehamat Shibasaki.

"It's one of those things that you just keep competing – keep the ball alive. It was still in the field of play so you do what you can do to get it down," he said.

"It was just fortunate it paid off."

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It was one of many bright lights in the Sea Eagles' performance as they came from behind twice to lead the Knights until the 72nd minute when Kalyn Ponga and Enari Tuala combined for the match-winner.

"There's a lot of shattered boys because everyone put in a real effort and it didn't come off," Cust said.

"We'll train hard this week. The Souths game is very important for us. I'm looking forward to it already."

Manly are now 10th – four points adrift of the top-eight with six games to play to try and force their way into the finals.

On the horizon after the Rabbitohs, are the Storm and the Wests Tigers, who are tied on 12 competition points with Manly in the race to jag the remaining playoff berths.