The Red Devils have been in sensational form so far this season, winning six and drawing one in the Premier League.
They are second in the league, behind fierce rivals Manchester City on goal difference by one goal.
It bodes well for the 20-times league winners, who have seen signings Romelu Lukaku and Nemanja Matic bed in instantly.
Since his £75m move from Everton, Belgian striker Lukaku has scored 11 times.
But boss Mourinho is not convinced his much-improved side have what it takes to go the whole way this season.
He has even suggested that their place in the top-four is not even certain.
He told Portuguese outlet Record: “Last year the season started much harder and ended very well, this year it started very well and we don’t know how it will end.
“In another league it could be said that a team that starts with seven wins and a draw would almost mean the title.
“But in England it doesn’t mean anything, not even that we will finish in the first four places.”
Mourinho is the club’s fourth manager in as many years after Sir Alex Ferguson called time on his trophy-laden tenure.
In his final year, Fergie won the Premier League in what would be the last time the club lifted the cup before handing the reins to David Moyes in 2013.
