Erik ten Hag says Manchester United must respond with character and togetherness after a galling loss to Brighton on an afternoon when he regarded the booing of Rasmus Hojlund's withdrawal as a positive.
After a promising first season under the Dutchman, a number of off-field issues at Old Trafford have been compounded by poor performances and results on the pitch.
Already beaten away to Tottenham and Arsenal, Saturday's meek 3-1 home loss to Brighton meant the Red Devils have lost three of their first five matches for the first time in the Premier League era.
"Definitely that is something that bothers me," manager Ten Hag said of the results. "But also I have to see the way we play.
"But finally it's about character then. Now we have to see how strong we are, how the team sticks together and which players are standing up and showing the character and leading the team.
"Because in all the games, all the games but especially the games today, against Arsenal and Forest, we have seen we can play very good and we can create a lot of chances.
"But, yes, there are also some improvements to make. That is definitely the case and now we have to step up."
Danny Welbeck put Brighton ahead against his former club before Marcus Rashford's effort was deflected onto the woodwork and Hojlund's first goal for his new club was ruled out by the VAR.
Pascal Gross and substitute Joao Pedro put the visitors further ahead in the second half at a stunned Old Trafford, where substitute Hannibal Mejbri's exceptional first United goal did little to lift the mood.
There were boos at the final whistle and even louder jeers earlier in the second half when Ten Hag replaced lively full debutant Hojlund with Anthony Martial.
"I think it was positive," the manager said of the reaction to the substitution. "You see that the fans from the first moment in Old Trafford, the reception for him was great.
"I think he performed very well, so I think it's good that they gave this signal, this message. It will give him belief, Rasmus.
"But everyone knows he came in with a small issue. We built him over the last three, four weeks.
"He's not ready for a whole game and we have many games to play in short notice, so we have to build him also in fitness."
It has been a poor start to the season in all departments, but Ten Hag dismissed the notion that United are in crisis ahead of Wednesday's tough-looking Champions League group opener at Bayern Munich.
"No, but we have to be very disappointed," he said. "And we have to be very annoyed with ourselves because at United the demand is you win games."
This loss ended United's 31-match unbeaten home run in all competitions and saw them lose a Premier League match at Old Trafford for the first time since Ten Hag's opening game.
Brighton were the victors that day and celebrated a second-ever Old Trafford win on Saturday, when they made it four top-flight wins in a row against the Red Devils.
Roberto De Zerbi's brilliant side shone despite making six changes in the north west against a side constructed at a far greater cost.
"The football is nice because the small team can win in every moment against a great team," the Brighton boss said.
"But I think Brighton is becoming not a big, big team but it's not a surprise.
"The quality of the players of Brighton is very high and the organisation of the club. The possibility to manage two players per position is difficult.
"I don't know the problems of Man United. I can explain my team.
"We are used to working in our style, we are playing with courage because we defended in Old Trafford man-to-man all the time."