United fell 11 points behind Manchester City in the race for the title after losing 2-1 to their bitter rivals earlier today.
And Sunday Times reporter Duncan Castles claims Mourinho has set his sights in bringing in a new left-back, a winger and a central midfielder next month.
“Those are three positions Jose Mourinho feels have to be strengthened (left-back, central midfielder, winger) in January or the next summer window," Castles said, speaking on the Transfer Window podcast.
“We know he would have done the winger in the summer if possible. It's very hard to see them getting all three in this window.
“My information is he would be happy to get two of those positions filled in January if he can."