Frustrated supporters roared for the Dutchman to be sacked after Saturday's 1-0 loss at Old Trafford, but he still holds the reins despite media speculation he had offered to resign.
That may change if second tier Derby knock United out of the Cup, especially given mounting speculation that the club have lined up Jose Mourinho as their next manager after the Portuguese was sacked by Chelsea last month.
Derby were riding high in the Championship at the end of last year but Paul Clement's men have recently lost their way. Their only win in five matches in 2016 was a 2-1 victory over Hartlepool in the last round of the Cup.
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However, United captain Wayne Rooney, who scored a stoppage- time penalty to squeeze past third tier Sheffield United in the third round, knows the 11-times Cup winners cannot afford to be as erratic as they have been in the Premier League, in which they lie fifth.
"Derby have nothing to lose. No-one is expecting them to win and they will try to cause an upset. We know that and have to be ready for that," Rooney told MUTV.
Milton Keynes Dons are another Championship side facing elite opponents as they take on Chelsea on Sunday for a place in the fifth round.
With Chelsea playing catch up after a poor start to the season -- they are in 13th place in the Premier League and their League Cup title defence ended in the fourth round -- their only chance of salvaging silverware on home soil is the FA Cup.
Since Guus Hiddink took charge over a month ago following Mourinho's sacking, Chelsea are unbeaten in all competitions.
"We have to try to win the games we have left in the league, we are working very hard and I think it shows on the pitch," goalkeeper Thibaut Courtois told Chelsea's website (www.chelseafc.com).
Champions Arsenal will take on second tier Burnley on Saturday as they try to take another step towards becoming the first club since Blackburn Rovers in 1886 to win the FA Cup three years in a row.
A packed Saturday schedule will also feature three all-Premier League ties, Aston Villa v Manchester City, Crystal Palace v Stoke City and Liverpool v West Ham United.
Third-round giant-killers Oxford United will be eager to build on their win over Swansea City when they host second tier Blackburn Rovers.
(Editing by Ed Osmond)
