Steve Bruce admitted he was surprised at how his side struggled to cope with switching to a flat back four in their last game against Leicester City.
The Magpies have been well-drilled in recent years after operating with a back five under Rafa Benitez.
But as Bruce attempted to address the run of negative results he switched things to a more traditional formation, only for the system to backfire badly in a 5-0 loss at Leicester City last Sunday.
Bruce is toying with the idea of going back to a back five with left-sided Dutchman Jetro Willems available again to him for the clash with Manchester United.
When asked if he was taken aback by his side's inability to cope, he said: "We changed to a back four.
"They have all played in a back four, I am sure about that.
"Emil Krafth has played 25 times for Sweden there as a right-back, you have two centre-backs who are international footballers, and Paul Dummett has played left-back all his career.
"So we've changed to a back four and of course we were beaten - badly beaten.
"Yes we changed tactically because we didn't have a left wing-back.
"It's food for thought for me but we'll see what happens this week."
