Sir Jim Ratcliffe is one of Britain's richest men, according to Forbes
United's owners the Glazer family said in November that they were considering selling the club as they "explore strategic alternatives".
Ineos said the company had "formally put ourselves into the process".
Ratcliffe made an unsuccessful late £4.25bn offer to buy Chelsea last year after owner Roman Abramovich put the London club up for sale.
-- Courtesy of BBC Sport