The talented Belgium international is currently sidelined after breaking a bone in his foot, but was the subject of considerable interest in the summer.
Defour has previously attracted the attention of Liverpool, Arsenal and Manchester City, while Everton had a £9million bid for the player rejected in the close season.
Liege are under no pressure to sell as Defour is under contract until 2013, while a move in January is prohibited in any case by his injury.
It would appear though that United could be weighing up a move in the summer as Ferguson has moved to reassure Defour of his interest.
The letter, which has been released to the media, reads:
"Dear Steven,
I have just heard about your injury and, in the name of Manchester United, I would like to wish you a full and speedy recovery.
"I am sure at the moment you must be feeling awful and that you'll have all kinds of questions.
"Steven, these are natural worries but I have to tell you that modern medicine and treatments are incredible, you have to have confidence in them.
"I'm going to follow your progress closely and I will remain in contact with your club to have news of your recovery."
Defour was delighted to receive Ferguson's letter but the 21-year-old was swift to point out that the Premier League club had done everything by the book and had sent it to his club to pass onto him.
"One thing I should like to highlight is that Ferguson has followed his interest officially," Defour told Het Laatste Nieuws. "He addressed the letter to Standard.
"I think the attention is great, but I do not want people to think I am already at Manchester, which is by no means the case.
"But if they come knocking, then I would obviously not cause problems."
Defour, who is rated as one of the most promising players in Belgium, is targeting the match against Anderlecht on 16th January for his comeback date.
