The Sunderland manager believes that the pressure is getting to a bunch of players who cannot buy a win at the moment and who are coping with the unhappiness of understandably unhappy fans.
Supporters have not seen a Sunderland win in the Premier
League since the middle of November, when Arsenal were beaten at the Stadium of Light.
He said: "There are two types of courage in football.
"There's the courage to get stuck in, to throw yourself into challenges and compete, to keep on going if you get a cut or a kick – and, to be honest, you expect that in your players.
"But there's also the other courage.
"The courage to be there to receive the ball and want it when things are going against you, the courage to try and play football, to put your foot on the ball, when the pressure is there on you and your team-mates.
"And that's what we need."
Bruce will consider changing his selection for tomorrow, offering opportunities to those who feel they can turn things around for Sunderland, given their chance.
But he would have had to make one change regardless, with Jordan Henderson sustaining ankle damage which could bring his season to a premature end.
Kieran Richardson and Anton Ferdinand, though, are close to returning.
Bruce admitted: "As a manager, when things aren't going well, you can always change the personnel and I'll look at freshening us up for Tuesday.
"We have players champing at the bit to play and maybe I'll look at that too, the likes of Kieran Richardson and Anton Ferdinand.
"We've got a big, big game at Portsmouth, so we can't afford to lick our wounds too long.
"Hopefully we can get our key players firing on all cylinders and those coming back from injury available again and go again.
"The one thing we have to do as a team right now, is to have a belief in ourselves.
"Whoever comes into the club has to know there's a big, expectant demand here and you have to be a big player to handle it.
"The Stadium of Light tests you and that's not going to change.
"I asked my players to appreciate that at half-time – I didn't rant and rave, quite the opposite in fact – I just told them to calm down and stop being so nervous.
"With the greatest of respect to Michael Turner, he didn't get boos at Hull if he miskicked a ball.
"But there's a different expectation at Sunderland and rightly so.
"Matt Kilgallon has just come in and I can understand him being a little nervous, Alan Hutton has just come in, too, and he's got to match those expectations quickly.
"That's just the way it is at a big club, you have to have a big club mentality."
