The Red Devils have already completed deals for Shakhtar Donetsk midfielder Fred and Porto right-back Diogo Dalot.
And according to the Manchester Evening News, Mourinho is keen to splash the cash again.
They say United want another centre-back, a central midfielder and a striker to push Romelu Lukaku at Old Trafford.
MEN say Mourinho has cooled his interest in a left-back, with the Special One keen to strengthen elsewhere.
Mourinho is also desperate to sign another central midfielder should Marouane Fellaini quit Old Trafford this summer.
The Belgium ace is likely to leave at the end of the month when his contract expires.
United have held talks with Tottenham defender Toby Alderweireld, 29.
Spurs are said to be resigned to losing the Belgium international this summer, with the centre-back out of contract next year.
Tottenham are demanding around £70m for the defender, with United only willing to pay £50m.
MEN add that United have also spoken with Willian’s representatives.
The Chelsea star has been linked with a move to Old Trafford in recent weeks, with Mourinho keen to reunite with the Brazil international.
Mourinho watched United’s arch-rivals Manchester City storm to the Premier League title this season.
Pep Guardiola’s men broke the 100-point barrier on their way to the title.