The Daily Express is reporting that Mourinho feels part of the issue of late is that his players still feel they are in a 'straightjacket' applied by former boss Louis van Gaal.
The report indicates that United players are battling to move past van Gaal's possession-based game and are yet to fully take up Mourinho's more direct approach.
A run of three straight losses shows that the Red Devils are well below par following a promising start to the season under Mourinho who feels that the squad is experiencing a delay in moving past the tactical demands of the departed Dutchman.
Mourinho reportedly wants United to be quicker in their transition from defence to attack after van Gaal had his side keeping the ball at their feet and knocking it around ad nauseam.
Many critics feel the Portuguese is struggling to fit big-name summer signings Zlatan Ibrahimovic and Paul Pogba into the same line-up as captain Wayne Rooney with a number of pundits calling for Michael Carrick to be deployed alongside Pogba.
Just another problem the 'Special One' needs to solve at Old Trafford...
United, who have been beaten by Manchester City, Feyenoord and Watford in their past three games, meet League One club Northampton Town at Sixfields Stadium in the third round of the EFL Cup on Wednesday night.