The Flyers did not reveal specifics of what was discussed at the meeting, but several veteran players voiced their disappointment with the loss in Florida.
"It's Game 2, and you lose 7-1," defenseman Mark Streit told reporters. "I think we'd better have a little talk here."
"I don't think it was necessarily about the score, I think it's about how we played," All-Star right wing Jakub Voracek said. "I don't think we should be in that situation, to lose 7-1 in Game 2."
Hakstol, who was hired in May after spending the previous 11 seasons at the University of North Dakota, also was "disappointed" with Saturday's loss but said that he did not have a problem with the players-only meeting.
"The one thing that is absolute is that nobody is going to overreact," he said. "You take this situation and deal with it for what it is. Deal with it honestly. Most of those dealings will take place in the locker room."
The Panthers scored four goals against goaltender Steve Mason in the opening 6:46 of Saturday's game, a modern NHL record for the fastest four goals to start a season, according to Elias Sports Bureau.
Streit was surprised by the blowout following Philadelphia's hard-fought 3-2 overtime loss in its season opener against Tampa Bay.
"For me, it's tough to explain because we had a really good game in Tampa against a really good team," he said. "[We] had a really good start, had a really good 60 minutes and got a point. Tonight it was like a different team out there."
Information from The Associated Press was used in this report.