Manchester United’s players may be struggling under the pressure of playing for the 20-time English champions, says manager Jose Mourinho.
Sunday’s 3-1 defeat at Premier League rivals Watford means United have lost three successive matches.
They are seventh with nine points from their opening five games, and lost their opening Europa League game.
“I feel that some individuals probably feel the pressure and responsibility too much,” said Mourinho.
“We have to improve, no doubt, individually and collectively. And that’s my job.”
The Red Devils won the Community Shield and their opening three league games under former Chelsea and Real Madrid manager Mourinho, who replaced the sacked Louis van Gaal in the summer.
But defeat by neighbours Manchester City at Old Trafford last weekend was followed by a disappointing Europa League loss at Feyenoord on Thursday.
Mourinho has lost three consecutive games in a season for the first time since February 2002, when he was Porto boss.
On Sunday, Watford led through Etienne Capoue’s first-half strike, only for teenage United striker Marcus Rashford to level from close range.
Hornets substitute Juan Zuniga scored with seven minutes to go and Troy Deeney added an injury-time penalty.
“We started the season very well with winning the Community Shield and three victories in a row in the Premier League, the best start that a new manager has had at Manchester United I think,” said Mourinho.
“But was I thinking that my team was ready, perfect, unbeatable? Not at all.
“I was completely aware that we were not perfect, with lots of players who are not end products and can make their own mistakes.”
Mourinho believes his team have been punished by a number of unfair refereeing decisions in their recent defeats, claiming they were also harshly treated against Watford.
The Portuguese manager thought there was a foul on Anthony Martial in the lead-up to Watford’s first goal when the United forward was dispossessed by home midfielder Miguel Britos.
Mourinho also claimed United were denied a penalty in the 2-1 derby defeat against City, while a Feyenoord player appeared to be offside in the build-up to their goal in the 1-0 win.
“The referee’s crucial mistakes are not in my control – there is nothing I can do about that,” said Mourinho.
“That is not under my control. So we were punished by these mistakes and I can’t do anything about it.”