The Daily Mail says United will write to Blatter this week after he waded into the furore over Cristiano Ronaldo's future.

He described United's stance over Real Madrid's pursuit as 'modern slavery' and the player subsequently agreed with Blatter's comments, which prompted United boss Sir Alex Ferguson to cancel a clear-the-air meeting with his Portugal winger in Lisbon today.

United will cite the apparent double standards Blatter has expressed. In February of this year, the FIFA president backed the sanctity of players' contracts with clubs after the Court of Arbitration for Sport reduced Andy Webster's fine from £625,000 to £150,000 for ripping up his deal with Hearts to move to Wigan.

"The decision which CAS took is very damaging for football and is a pyrrhic victory for those players and their agents who toy with the idea of rescinding contracts before they have been fulfilled," Blatter said at the time.

But, discussing Ronaldo last week, he said: "I'm always in favour of protecting the player and if the player wants to leave, let him leave."

United could be forgiven for thinking Blatter's sympathy for Ronaldo has something to do with his soft spot for Real, who made him an honorary member in November 2006 and presented him with a gold and diamond club insignia.

Real president Ramon Calderon revealed Blatter was a fan in his teens and, in a gushing response, the FIFA president said: "Allow me to again relay my sincere gratitude for the warm welcome, the incomparable hospitality, and the honourable distinction."