According to the French newspaper Le 10 Sport, Rybolovlev has told United and Real Madrid that 'James Rodriguez is [worth] €90m.' The Colombian international has been sensational at the World Cup in Brazil, and has a large number of Europe's top clubs keen to sign him this summer.
Real Madrid and United are the two leading contenders to bid for the 22-year-old, but the likes of Paris Saint Germain and Barcelona are also likely to be keeping tabs after a series of spectacular performances from Rodriguez in Brazil.
The attacking midfielder is currently the top scorer at the tournament, with five goals so far, including a goal of the World Cup contender against Uruguay in the 2-0 victory over their South American rivals in the last 16.
He leads Lionel Messi, Thomas Muller and Neymar, who all have four goals as the tournament approaches the quarter-final stage.
Monaco: Tempted to sell?
The Ligue 1 money-bags signed Rodriguez for €45m as part of a double deal from Porto involving Joao Moutinho as well. After a brief spell playing in Argentina he made the move to Europe and has flourished in both Portugal and last season in France.
But Rybolovlev is looking to at least double his money before agreeing to sell Rodriguez on - after all, the Russian billionaire has no financial motivation to sell.
€90m would also be approaching the world record transfer fee, which is Gareth Bale or Cristiano Ronaldo's move to Real Madrid depending on the report you read.
United busy in the transfer market
The fact that Louis Van Gaal is still at the World Cup with the Netherlands has not stopped United from getting the signings in early - Ander Herrera and Luke Shaw have already joined.
Reports claimed before the tournament that United have serious money to spend this summer - up to £200m - which means they could be in play for Rodriguez too.
Real Madrid are always in these kinds of conversations, and with Luis Suarez looking more likely to join Barcelona, they may switch their attention exclusively to the World Cup's stand-out player.