Peter Beardsley's second-string were due to take on their Southampton counterparts at Whitley Park on Monday, 27th February.
But with United in FA Youth Cup quarter-final action against Tottenham that evening - and the Saints' first-team facing Manchester United in the EFL Cup final on Sunday - the match has now been moved.
It will now take place on Tuesday, 28th February. Kick-off at Whitley Park is at 1pm.
A victory for Newcastle would see them finish top of Group A and take them into the next round.