Sam Allardyce is losing sleep because of the stress and "burden" that comes with trying to keep West Ham in the Barclays Premier League.
United take on Manchester City in the second leg of their Capital One Cup semi-final on Tuesday.
Ordinarily, for a team that has not won a major trophy for 24 years, a domestic semi-final would be something to shout about, but Hammers fans are bracing themselves for another hiding after they lost the first leg 6-0.
West Ham's league form is of deep concern to Allardyce, as well as the club's fans and owners, too.
The east London club slipped into the relegation zone on Saturday following a 3-1 defeat to Newcastle and Allardyce has been tossing and turning at night as he contemplates the task ahead of him.
"You lose a bit of sleep and you don't sleep quite as well as you would like to," the West Ham manager said when asked how he was coping.
"Saying that, you don't sleep much as a manager anyway."
With games against Manchester City, Tottenham, Manchester United, Arsenal and Liverpool in their final eight Premier League matches, Allardyce knows his team must start winning games fast.
The good news for the Hammers boss is that Andy Carroll has reacted well to his introduction back into the first team.
Carroll has come off the bench for West Ham in the last two games following an eight-month spell on the sidelines and he will feature against City on Tuesday.
Allardyce confirmed that Ravel Morrison will play and that Ricardo Vaz Te is fit again after three months out with a shoulder injury.
A place in the final is surely beyond West Ham, but Allardyce wants to see some fight from his players against Manuel Pellegrini's side.
"It's highly unlikely we will get through," Allardyce said.
"But we are at home, we are playing for pride and will try to play well and get a result."
Meanwhile, Pablo Zabaleta insists Manchester City will not be going through the motions as they look to rubber-stamp their place in the final.
City are all but guaranteed to be playing at Wembley after thrashing the Hammers a fortnight ago.
With such a commanding advantage, manager Manuel Pellegrini is likely to rest a number of key players at Upton Park but Zabaleta claims there will be no complacency.
The right-back, one of those who may be given a night off, said: "It doesn't matter about the first leg.
"We have to go into that game thinking it's a new game, even though we have six goals.
"We need to try and win it, like we are doing in other games at the moment. We are winning games and working hard.
"West Ham are in a tough moment, they are at home and will want to win it. So we need to take it seriously and we will."
City manager Manuel Pellegrini is also taking nothing for granted.
He said: "We have to play on Tuesday. The semi-final is not finished.
"Of course we have made an important step (towards the final) but we must see which players will play and the way we will do it."
Two players who could come into the reckoning for City are striker Stevan Jovetic and midfielder Jack Rodwell.
Both have been hampered by injuries throughout the season but are thought to be close to fitness.
Montenegro forward Jovetic has almost become the forgotten man since his B£22million move from Fiorentina last summer.
While fellow forwards Sergio Aguero, Alvaro Negredo and Edin Dzeko have scored 58 of City's 103 goals this season between them, Jovetic has claimed just two from five appearances.
Hamstring and calf injuries have been his main problems but Pellegrini has repeatedly stressed his importance to the squad for the second half of the season.
England international Rodwell has made just three starts this season after more of the hamstring problems that have blighted his career.
When asked if either had a chance of playing at West Ham, Pellegrini said: "Maybe, we will see. On Monday we will decide."