The Red Devils sold the 24-year old to Turf Moor for just £2m in 2015, but they will have fork out £25m to bring him back this summer, according to the Daily Mail.
Keane is reportedly keen to re-join the club he has supported since he was a boy. The Stockport-born centre half, who made his England debut in March, had been with United since he was 11, until Louis van Gaal shipped him away after making his loan deal with Burnley permanent.
Due to a 25-per cent sell on fee in Keane's contract, the transfer will cost less for United than any other club looking to buy the defender.
It is expected that the Red Devils will quadruple Keane's £25,000-a-week wages if he moves back to Old Trafford.