Simon Grayson warned his Leeds players he is ready to wield the axe after a humiliating 4-1 defeat at Yorkshire rivals Barnsley.
Grayson has come under fire in recent weeks as Leeds slipped away from the play-off places and the embarrassment at Oakwell prompted a furious response from the Leeds boss.
He knows chairman Ken Bates will be ready to consider a change of manager if Leeds are unable to reverse a run of four games without a win and made it clear several players who featured on New Year's Eve may not get another game for the club in 2012.
Ricardo Vaz Te's hat-trick and a fine strike by Craig Davies did the damage for Barnsley and Grayson said: "There are so many words you can use to describe the performance. Embarrassing, shambolic, too many to say.
"When you play for Leeds United you have to earn the right to wear the shirt. Too many of them didn't do that and that's embarrassing. A lot of stuff is going to have to happen over the next couple of days.
"Any footballer can have a poor day at the office, but unless someone chops your legs off, you can run around. It's embarrassing to be the manager of the club. One or two might not play for the club again.
"Every one of the players has to look themselves in the mirror and be embarrassed by what they've done today and make sure they do something about it on Monday.
"I want to get to the Premier League with this club and my staff do. One or two players are too comfortable in just earning their money and they have another thing coming."
West Ham manager Sam Allardyce admitted his patched up team paid the price for a disastrous start that gave Derby a deserved 2-1 win at Pride Park.
The Hammers were ravaged by suspensions and injuries and it showed in the first 10 minutes when Derby scored twice through Callum Ball and Paul Green.
Frank Nouble scored his first goal for West Ham just before half time but the promotion favourites slipped to third place after missing a chance to draw level with leaders Southampton.
"The disaster in the first 10 minutes made it too difficult for us," Allardyce said.
"We didn't make life easy for ourselves, we knew we were putting a team out that was patched up and the last thing we wanted to do was to give the opposition a couple of goals. It knocked the stuffing out of us."
Middlesbrough moved above West Ham into second place but boss Tony Mowbray was in no mood for celebration after a 1-1 draw at home to Peterborough.
Boro were denied a share of the top spot when Tommy Rowe's 87 minute equaliser cancelled out Scott McDonald's opener for the hosts.
"That felt like a defeat," Mowbray said. "We dominated the game for long spells, we had I don't know how many efforts on goal and we hit the woodwork twice so of course we come away frustrated.
"We had in mind that Southampton and West Ham had both lost but we've said before, it doesn't matter what the other teams do, you still have to go out and win your game and we didn't do that."
Elsewhere, fourth placed Cardiff boosted their promotion push with a 1-0 win at struggling Nottingham Forest, while Reading are fifth following a 1-0 victory over Ipswich.
Birmingham beat Blackpool 3-0, Crystal Palace won 1-0 at Millwall and Leicester drew 1-1 with Portsmouth.
Doncaster slipped to the bottom of the table with a 4-1 loss at Watford and Coventry improved their survival chances by beating Brighton 2-0.