"You see the level of the teams - you see Liverpool's squad, Manchester City's squad, Chelsea's squad, Tottenham's squad, and Arsenal are improving".
Mourinho believes any post-Russia hangover is mental rather than physical, with World Cup victor Paul Pogba inspiring United to victory in their Champions League opener at Young Boys.
"I am optimistic, but a hard season, yes", he said.
United's run of form - three wins from three away games - has been built on an improved defensive record.
"I think it is (a mental thing)", he said.More news: Pakistan Slams India for Cancelling New York Talks
'I think we are going to be a better team.
"Every player has another level to step up", he said.
"He has recovered totally and Tuesday he plays again but he showed for the ones that don't know him very, very well he is not a player to be here just on formation, he is a player to be here for positions".
"A team that yesterday looked very bad, today looks very good and yesterday looked very good, today looks very bad".
Macari has been left impressed with the quality of football the team from the Black Country have displayed this season and admits that they deserved more than just a 1-0 win over Burnley last weekend.
Pogba played a crucial role in France's path to being crowned world champions - scoring a sublime goal in the final against Croatia - in Russian Federation in July.
"It's more about the moment and the momentum is very important in the positive and negative way".