David Moyes feels West Ham's main problem since he took over has been individual errors.
The Hammers were thrashed 4-0 at Moyes' old club Everton on Wednesday evening, and he has also overseen a 2-0 loss at Watford and a 1-1 home draw with Leicester following his appointment as Slaven Bilic's successor.
That has extended West Ham's winless run in the Premier League to seven games and they sit 18th in the Premier League table, two points adrift of safety.
And Moyes has warned his players the mistakes need to stop or he will look for new players.
He said after the match at Goodison Park: "I thought we were completely submissive in the first half and the worst thing was individual mistakes cost us.
"I think in the time I've been here, in the three games I've had, the goals we're conceding are from individual (errors).
"I don't think it is because we are not organised or not running hard enough to get back into position, or the players are not showing the right attitude.
"I actually think it was individual mistakes in the games that are costing us, so we either have to eradicate it or find people who are not going to make the individual mistakes."
West Ham were 2-0 down at the break following a brace from Moyes' former player Wayne Rooney, who subsequently completed his hat-trick with an outrageous strike from just inside his own half, before Ashley Williams headed in Everton's fourth.
Manuel Lanzini missed the chance to make it 2-1 early in the second half when his penalty was saved by Jordan Pickford.
The east London outfit are next in action when they face unbeaten league leaders Manchester City away on Sunday.
And Moyes added: "I think I have got to hope that this is where 'you never know what happens in football' comes in, because we certainly wouldn't be looking favourites.
"But I have to say there's not many teams looking favourites when coming up against those teams just now.
"We have to go there and it's exactly right - you never know."
After Winston Reid came off in the second half of Wednesday's contest, Moyes said it appeared the defender had tweaked his hamstring.
He also revealed Andy Carroll had sat out the match having jarred his knee in training, and said: "We don't think it's that bad. We had it scanned and nothing showed up."