A furious Trent Barrett has labelled his side as "not being able to handle any adversity" and "capitulating" as Manly squandered a 20-point lead against the Panthers to darken the storm clouds circling Brookvale.

Already wrestling with news police are investigating match-fixing allegations involving the Sea Eagles in two games last year, Manly surrendered a seemingly impregnable lead as Penrith secured an unlikely win on Sunday.

The Panthers roared back into the contest with 27 points in the final half hour to run out 31-24 winners and condemn the Sea Eagles to their seventh loss in their last eight matches.

And an agitated Barrett didn't hold back, defending the commitment of his players during the week but questioning their mental fragility with half of the squad's salary cap sidelined through the likes of Daly Cherry-Evans, Jamie Lyon and Steve Matai.

"There's just a 15-minute period where we just capitulate and we can't handle any adversity," Barrett fumed. "That's what happened again. We've got a lot of young players there who are still learning to be first graders and to be a first grader and to win consistently at this level you have to be able to play for 80 minutes. And we can't.

"Until we do we're going to be on the end of that again. The players are sick of it and I know they're trying hard, but unless we learn to do it we'll be sitting here again."

Former Prime Minister and Manly's No.1 ticket holder Tony Abbott took his leaving cue while Manly were ahead 24-4 shortly after the break, but he wouldn't have been impressed with news of Penrith's incredible revival. It has turned up the heat on the Sea Eagles, who plunged further out of the finals picture and face a testing trip to the Gold Coast next week.

"The way they handled themselves off the field is a credit to the players," Barrett said. "I'll never question their effort and their commitment to what we're doing. They work bloody hard all week.

"That's what shits me the most is we put ourselves in a position to win on the back of how hard they've worked and throw it away as easily as what we have. We're missing $3.5 million worth of players. Let's not forget that. But we were still in a position to win and that's the frustrating thing."

NSW utility Dylan Walker delivered a first-half masterclass to enhance his case for re-selection in game two and Barrett bristled at criticism of his nine-minute cameo on debut in the Origin opener.

"I thought it was ridiculous the criticism he got," Barrett said. "He had nine minutes on the field. What did you want him to do? You would have criticised Laurie [Daley] if he didn't pick a utility on the bench and we got an injury in the backs in the first two minutes. You can't have it both ways."

Barrett and Queensland will sweat on the fitness of Nate Myles, who limped off with a knee injury before returning in the second half.

Penrith coach Anthony Griffin admitted he thought his side was "a rough chance" even when trailing by 20 points and hailed the character of his side featuring second-gamer Nathan Cleary and NSW player of the future Bryce Cartwright in the halves.

"I don't think we've ever lacked belief and on the outside you see the scoreboard every week, but on the inside we've got simple standards and some weeks we're getting them and some weeks we're not," Griffin said.

"That's as bad as it gets being down by 20 against Manly on a Sunday."