McFadden acknowledged concerns over Mannering's physical state were a talking point but insisted he would not be pressuring him to rest, after Herald columnist Chris Rattue suggested New Zealand league would benefit if Mannering stayed home in November.
"I have seen that speculation but certainly I won't be getting involved. If he wants to go on that tour then he'll go," he said.
"Simon's earned the right to make his own decisions and I'd never ever try to influence him any other way so that will be a decision he makes."
After captaining the Kiwis to Four Nations glory at the tail end of last season, Mannering has backed up to play all 22 games for the Warriors so far this year, and the Anzac test win over the Kangaroos.
Never one to make much fuss, he struggled through a period early in the season with a gastro bug that saw him rested from some team training and even replaced late in matches against Wests Tigers, Cowboys, Rabbitohs, Titans and Raiders.
McFadden said Mannering's absence from today's field session was just a part of managing his workload, while fullback Sam Tomkins and Bodene Thompson also withdrew to rest and apply ice to different bumps and bruises.
"He's done a lot of work this year so we've just got to try to get him feeling fresh for this weekend," he said.
"It's that time of year so we've just got to manage this. We've still got to be smart about the way we prepare so a couple of guys we pulled out but we'd planned to do that and we'll be fine.
"We're going to have to really find some creative ways to get ourselves up this week but the training session there today shows me that they're still ready to play footy this week."