A minority shareholder deal is in the works between the British billionaire and the Glazer family, which is expected to cost in the region of £1.25billion.
According to Sky News, an additional £245m will then be put into the physical infrastructure of the club.
The money is set to come from Ratcliffe's personal wealth in a clear break from the Glazers, whose investment has often come by loading debt onto United. It will also be paid in installments to be largely completed by the end of the year.
It is said that the money will not be put into United's transfer budget and playing squad.
That is despite talk of Ratcliffe taking responsibility for the Red Devils' on-pitch activity when his share purchase is sealed, potentially in the next fortnight.
Erik ten Hag's side are labouring outside of the European qualification places in the Premier League having also struggled in cup competitions.
However, the state of Old Trafford has long been pinpointed by fans as a key area of the Glazers' failings while in charge of United.
A lack of major upgrades to the 74,000-capacity stadium since its latest expansion in 2006 has led to complaints over a leaking roof and the quality of facilities in and around the ground.