Henry, revered in New Zealand for guiding the All Blacks to their drought-breaking World Cup win in 2011, started a month-long stint as a coaching consultant at the Warriors this week.
The NRL team sanctioned six players for breaching team protocol last week after media reports that five of them had taken prescription drugs mixed with energy drinks on a night out in Auckland following a heavy loss against Melbourne Storm.
Three of the players were banned from representing New Zealand in a match against Australia last week.
McFadden said Henry's appointment had been decided well before the problems at the club emerged.
"This is something we've discussed right from the end of last year around bringing someone in the organisation who can add value," McFadden told New Zealand media.
"Obviously Graham's a very astute coach and an admired person but it also hasn't been all smooth sailing for him as well and that's what I want to draw on.
"We're going through a bit of a tough time but if you stick to what you believe in then you can come out the other side."
(Reporting by Ian Ransom in Melbourne; Editing by Peter Rutherford)
