Mourinho has repeatedly expressed his desire to bring in additional signings throughout the preseason with a central defender leading the way.
However, despite the links to numerous objectives, United still has to reinforce.
“The market closes today, it’s time to stop thinking about the market,” he said.
“I’m not sure, I have to concentrate on the players I have and the next games.”
So far, United have signed three players this summer: Brazilian midfielder Fred for 47 million pounds, Portuguese defender Diogo Dalot and third choice goalkeeper Lee Grant.
But Mourinho has been interested in strengthening his squad even more after finishing second last season, 19 points behind the champion, Manchester City.
Although there has been speculation about an agreement for Toby Alderweireld of Tottenham, there has been no offer from United, while Leicester remains determined to retain the English international Harry Maguire, who still has four years left on his contract.
The Portuguese manager also had to deal with a series of injuries to high-level players during the preseason.
Antonio Valencia and midfielders Nemanja Matic and Andre Herrera are among those absent for the first Premier League game against Leicester on Friday (20:00 BST).
But he hopes that some of his World Cup players will be available with Paul Pogba, Jesse Lingard, Ashley Young and Marouane Fellaini now back in training.
“Those who played late in the World Cup trained Monday, Tuesday, Wednesday, today,” he added.
“They’re not fit and ready, but we have needs, and I’ll talk to them today to see how available they feel they are.”