McFadden believes three players - injured winger Manu Vatuvei, centre Konrad Hurrell and departing utility Dominique Peyroux - let the club down by attending an R&B concert in Auckland last Friday night, when Hurrell and Peyroux should have been preparing properly ahead of their early morning flight to Sydney.
"When I first heard about that I must admit I was extremely disappointed," said McFadden.
"That sort of level of professionalism is unacceptable. We had an early flight the next day and one of the things we preach in terms of our preparation is that we get enough sleep, hydration and make sure we eat properly.
"I don't think that was acceptable. It's certainly something that we've looked at internally and that's how we'll be dealing with it too."
The situation was made worse by the players posting comments and video on social media, of them onstage in front of a packed crowd during R&B artist Ginuwine's live performance at Auckland live music venue The Studio.
McFadden felt the timing of the player's social media activity was poor, with the Warriors struggling for results after seven straight defeats.
"It's something we're going to have to continually remind players [about]," he said. "People are going to make mistakes in the future. They've made one this time and certainly the timing of all this is not ideal.
"It's going to put us under more pressure. It's something that we'll address with the players and that will be an ongoing thing."
He rejected suggestions that the players involved could have been stood down from Sunday's final round away clash with the Canterbury Bulldogs or fined, and despite his disappointment said their actions were not deserving of such punishment.
"I don't want to make a mountain out of a molehill either. On the seriousness scale it's only minor but still, it's unacceptable from our point of view.
"Hopefully it's something the rest of the group can learn from, but in terms of standing people down or fining, I don't think that's the answer."
Vatuvei, who is out for the rest of the year with a shoulder injury, had come in for further scrutiny after a tweet revealed he was not watching television coverage of the Warriors game, but at the cinema to watch the film War Room.
McFadden reiterated his disapproval and made the point that public perception and timing is everything at a time when the entire club is struggling.
"Timing's everything, isn't it? So [it's] not a good look. I haven't spoken to Manu about that yet so I'm sure I'll sit down with him and make everyone aware of what's appropriate.
"If we're winning no one is making these comments, but we've got to accept that the situation we're in, we haven't earned the right to be this flippant."
- David Skipwith of the New Zealand Herald
