Jack Colback described Newcastle's performance in a 5-1 loss away to Crystal Palace on Saturday as "embarrassing" and has questioned his team's strength of character.
Papis Cisse earned Newcastle an early lead, but Steve McClaren's men then collapsed as two goals apiece from James McArthur and Yannick Bolasie and a Wilfried Zaha strike saw the struggling visitors suffer another comprehensive loss.
The result leaves Newcastle second from bottom, two points off safety and with the prospect of a grim relegation battle in 2016 looking increasingly likely.
"We had a game plan and in the first 15-20 minutes it worked perfectly. We got the goal and you could see they were rattled,"Colback told the club's website.
"But we let them straight back in, then I made a mistake for the second goal and that put us on the back foot again. After that it was pretty embarrassing, really.
"Maybe we're not strong enough character-wise. It seems as if as soon as things go bad, it goes really bad. We had that last year and probably the year before as well. It's something that's hanging over the team that we need to get rid of.
"We had shown signs of improvement but the Leicester game and this one have really set us back quite a lot," he added, referring to a 3-0 loss at home to the Foxes in their previous fixture.
Newcastle's next opportunity to turn their dire fortunes around will come at home to Liverpool next Sunday.
