United have already signed Victor Lindelof and Romelu Lukaku in big-money moves this summer.
Those two men cost the Red Devils a combined £110m.
But, according to The Sun, their spending isn't set to end there.
They claim there is still more than £100m left in Mourinho's transfer kitty.
He is said to be hoping to spend £35m of that on Inter Milan winger Ivan Perisic.
But he also wants to bring in another defender as well as a holding midfielder.
An Old Trafford source told The Sun: “The club have already invested a lot into the playing squad this summer.
“But there is still a lot left in the coffers and it’s all there for Jose to spend on whoever he likes.
“Lukaku and Lindelof were just the start of what is going to be a busy summer at Old Trafford with lots of ins and outs.
"This is going to be a huge window for the club with loads of players leaving and plenty coming in as well."
