After a tough start to the 2018-19 campaign, the Red Devils are in sixth place in the table ahead of Sunday's trip to Liverpool and eight points off the UEFA Champions League places.
Despite their issues, Mourinho has said he's unclear whether he will be able to bring in new faces to bolster his squad, per Dom Farrell of Goal.
"I don't know if we are going to have new players," he said. "I would like to, but I don't know if it is possible or not. It depends on the club. Honestly, I'm focused on my job of playing Liverpool and next week playing Cardiff City. I'm more focused on that."
Ahead of the match with their big rivals on Sunday, the United boss made it clear that his squad is a long way short of what he expects:
In the summer, the Red Devils didn't make many high-profile signings. Fred was brought in from Shakhtar Donetsk but has struggled to settle in the English game, while the 19-year-old Diogo Dalot is beginning to get more minutes under Mourinho.
There has been some speculation United could add to their squad in January. According to James Robson of the Evening Standard, the Red Devils are interested in Napoli defender Kalidou Koulibaly and ready to spend around £100 million on him.
There have also been reports of potential outgoings, with Simon Mullock of the Sunday Mirror suggesting Paul Pogba will be up for sale in the January. Mullock said "Mourinho has run out of patience with the midfielder."
Bleacher Report's Rob Blanchette thinks United should be looking to build the team around Pogba:
While Mourinho clearly isn't content with his squad, there's no doubt he should be getting more from the players he has at his disposal. Under his guidance, the development of some star men has stagnated, and the style of football is often stolid.
Major deals have traditionally been difficult to get done in January, although Liverpool were able to bring in Virgil van Dijk in the previous midseason window for £75 million, and the Netherlands international made an immediate impact.
If United were able to add a player of similar quality, it would be a huge boost for Mourinho.