Sources have told ESPN FC that United are interested in central defenders Jerome Boateng, Toby Alderweireld, Harry Maguire and Yerry Mina but Mourinho - who has said the season could be "difficult" if the squad is not bolstered - admitted at a news conference on Thursday he is not expecting any new arrivals.
"Subject to any late sales, the Premier League and its clubs may benefit from having playing squads settled and in place for the start of the new season".
Part of this can be explained by the fact one of the 20 Premier League clubs - Tottenham - saw no incomings, the first time this has happened since the summer transfer window was introduced in 2003.
"I'm not confident", Mourinho said, when asked whether there would be more players arriving before the deadline.
The striker turned broadcast pundit believes Liverpool's mental edge over City following three victories against them last season - twice in the Champions League and once in the league - could be the difference if City do not runaway with the title in the manner they did last season.
"I am not confident, and the market closes today, so it's time, at least for me, to stop thinking about the market because the market will be closed". His side face Leicester City in their opening fixture at Old Trafford on Friday and it was put to Mourinho that there was a perception the club had gone backwards over the summer. 'When I listen, when I read, it's hard to believe we finished second because you are capable of making people who finish second (sound like we) were relegated.
Ander Herrera and Nemanja Matic are among six players ruled out of the game with injury, with captain Antonio Valencia, Marcos Rojo, Sergio Romero and Diogo Dalot also sidelined. Sometimes its also hard to believe I won eight championships and three Premier Leagues, and I keep thinking the second position a year ago was one of my biggest achievements in England'.
Mourinho also needs to check on the fitness of those that returned late from the World Cup. In football, you need time to work and players on the pitch to work and we didn't have until now.
The Arsenal legend said: "I want this season's title race to be more spicy and I think it will be".