Jose Mourinho has said three straight wins has not changed his opinion that Manchester United are in for a tough season.
The Portuguese coach predicted during the summer his team would face a "difficult" campaign and despite victories over Burnley, Watford and Young Boys, he has not changed his mind.
"I am optimistic, but a difficult season, yes," he said. "For sure difficult season. I don't change that because we won two matches in the Premier League. Difficult season for sure.
"You see the level of the teams -- you see Liverpool squad, City squad, Chelsea squad, Tottenham squad, Arsenal improving. It's going to be difficult."
Mourinho said his team will find it tough to top the 81 points they collected last term -- their best return since Sir Alex Ferguson retired in 2013.
United host Wolves on Saturday with the chance to win four games in a row for the first time since January, and Mourinho said he is confident his team have improved from last season.
"I am not saying we are going to have more points than last season because last season we collect a very acceptable level of points," he said. "I think we are going to be a better team. We are going to play better than we did but I think it's going to be a very difficult season.
"Not just for us, also for the others because the others they can say exactly the same as I am saying and they can say 'oh, Manchester United, good team, good squad, City good squad, good team'. All of them, they can say the same thing."
Mourinho confirmed Alexis Sanchez will start against Wolves despite watching from the bench against Young Boys as his replacement, Anthony Martial, scoring in the 3-0 win.
The Chile international is yet to score in four games this season and has managed just three in 22 games since arriving from Arsenal.
Mourinho refused to single out the 29-year-old but, in answer to a question specifically about Sanchez, challenged his entire squad to get better.
"Sanchez plays because Martial played 90 minutes [against Young Boys] and Sanchez played zero," said Mourinho. "Every player has another level to step up."
United have recovered from back-to-back defeats to Brighton and Tottenham in August to move back towards the top of the table.
Games against Wolves, West Ham and Newcastle offer a chance to close the gap on early leaders Liverpool and Chelsea but Mourinho has warned his players not to take their good form for granted.
Tottenham earned plaudits for their performance at Old Trafford but have lost their last three while Manchester City were shocked by Lyon in the Champions League on Wednesday.
"I think good results, good performances, they make miracles and bad results and bad performances, they make you look more tired, more upset, more ugly, more everything," Mourinho said. "Football is a little bit like this. A team that yesterday looked very bad, today looks very good and yesterday looked very good today looks very bad.
"I think this is more the influence of the moment. It's more about the moment and the momentum, like you like to call it, is very important in the positive and negative way."