Sharecast - According to Sky News, the agreement would see Ratcliffe's Ineos Sports acquire two boardroom seats at Old Trafford.
Ineos would acquire 25% of the listed A-shares, and the Glazer family, who have controlled the club since 2005, would sell 25% of their B-shares to Ratcliffe.
The deal also reportedly included a commitment from Ratcliffe to invest £245m into United's infrastructure, though more capital could be needed to bring its stadium up to elite football standards.
Ratcliffe's investment would not add to Manchester United (NYSE:MANU)'s existing debts, Sky reported, as he would personally finance the improvements.
The deal came after more than a year of exploration by the Glazers to sell a stake in the club, with several potential buyers considered, including Sheikh Jassim bin Hamad al-Thani.
It was reported that Ineos would immediately take control of the club's playing side.
Ineos and Manchester United had not commented on the impending deal as of lunchtime on Monday.
Reporting by Josh White for Sharecast.com.