Mourinho was eager to land a new centre-back all summer but the United hierarchy failed in their efforts to secure some targets and refused to deliver others.
There were murmurings after the August deadline passed that Raphael Varane was of interest but Real Madrid refused to sell, while other targets like Harry Maguire were vetoed at board level because it was believed they offered no upgrade on existing players.
United have since struggled defensively - leaking 17 goals in 10 games and keeping just one Premier League clean sheet so far - leading a report from The Guardian to declare that Mourinho will be backed in January to strengthen the squad 'if the right deal is possible'.
With United not able to land Varane and opting against seriously pursuing others, it is said that the same budget that was there to be spent in the summer is still available.
There is, however, no guarantee that United will definitely spend big in January as the mid-season transfer window can be notoriously difficult to navigate and come out with anything that resembles value, given that prices for top clubs are often at a premium except in rare cases.
The Sun has claimed that United are willing to splash out £60m on Maguire. The England international only recently signed a new long-term contract with Leicester after staying with the Foxes, but the gossip is that United could double his current £75,000-per-week wages.
Given that The Guardian gave no indication that United's stance on Maguire has changed since summer, stories of spending a vast sum on the 25-year-old Yorkshireman should perhaps be taken with a pinch of salt until there is any substance behind them.