Having signed Fred, Diogo Dalot and Lee Grant, the Portuguese hoped to bring in two more players but would have been satisfied with just one.
Mourinho had warned it would be a "difficult season" if United did not make any more acquisitions and it now looks like his side will miss out.
Asked if nothing would happen in or out before the Premier League deadline at 5pm, he said: "The information I have is no (nothing will happen)."
While United may have a quiet deadline, other clubs will certainly be busy - stay up to date with Sporting Life's Deadline Day blog, here.
United had been hoping to sign a centre-back before the deadline but hope has faded in recent days.
"I am not confident," Mourinho said.
"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."
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The lack of new signings will compound issues surrounding his squad for the start of the Premier League season.
Sergio Romero, Antonio Valencia, Marcos Rojo, Dalot, Ander Herrera and Nemanja Matic will all be unavailable for Friday's opener against Leicester.
Mourinho also needs to check on the fitness of those that returned late from the World Cup.
"They returned on Monday," he said. "They trained Monday, Tuesday, Wednesday and today, so you can imagine they are not really fit and ready.
"But we have needs.
"The list that I gave you before of the injured players is an important list and today after training I will speak with that group of players (back from the World Cup because everybody is different, physically and mentally, to see how available they feel they.
"Because it is very important their feeling and to understand how they think they can help or not help."
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