Steve McClaren faces "a massive job" motivating Newcastle players who are "letting him down big-style", according to Sam Allardyce.
Wednesday night's Capital One Cup defeat to Sheffield Wednesday brought boos from the St James' Park crowd and had McClaren admitting the club is "very close to a crisis".
The new manager has delivered just one win - against League Two Northampton - since succeeding John Carver in the summer despite shelling out big money on four new first-team players.
Chelsea visit on this weekend's Saturday Night Football and Allardyce, who lasted just eight months at Newcastle, told Sky Sports News HQ McClaren must urgently wring a result from his under-performing side.
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"Getting a win for Steve is the most important thing now," he said. "He's finding out how good his players are, and those players at the moment are certainly letting Steve down, big-style, letting themselves down and Newcastle down.
"So Steve's got a massive job to turn it around as quickly as possible, to really get into the players and tell them their responsibilities wearing that shirt in such a passionate city."
Newcastle supporters have long complained about a perceived lack of investment from Mike Ashley, but the owner this summer sanctioned the signings of Gini Wijnaldum, Florian Thauvin, Aleksandar Mitrovic and Chancel Mbemba.
And Allardyce believes his old club might actually have recruited too many new players at once.
He said: "The Newcastle fans were crying out over a lack of signings last year. Now they've gone and made those signings, and we all know one of the most important things is who you recruit when you're spending £30m, £40m, £50m.
"When players come from abroad you cannot really say whether they're going to be successful or not. You just hope they can take the form they've shown in the country they've been playing in into the Premier League.
"When you've got so many in such a short space of time that don't know each other's strengths and weaknesses it's a massive job for any manager. The only way Steve will get the time to do the job he wants to do is by making sure Newcastle start picking up some results."