كتب : Megan Detrie
"There is no agreement with Real and United over Ruud. We have refused their offer," the Manchester United boss was quoted as saying by The Guardian newspaper.
Ferguson was speaking after United's 1-0 win over Kaizer Chiefs on their week-long tour of South Africa.
Reports had implied that Van Nistelrooy was ready to sign for Real following a medical on Wednesday, but Real's rumored £10 million ($18.3 million) bid was not close enough to United's £15m valuation for the 30-year-old striker.
The Scott boss had compared Van Nistelrooy with Ukraine captain Andriy Shevchenko who joined Chelsea from Milan earlier this summer.
"When you see that Shevchenko went for £30 million, he's a similar age to Ruud and their record in Europe is almost identical, so you can absolutely guarantee that we're not going to give Ruud away," he said early on Tuesday.
Ferguson admitted last week that Van Nistelrooy had informed the club that he wanted to end his time at Old Trafford.
The Dutchman was left out of the side for the League Cup final and the rift between the forward and the manager escalated when Van Nistelrooy stomped off the grounds before Manchester United's final game of the season.
Ferguson seems to have little regret about parting ways with the striker, and instead has been considering possible replacements.
"We have options among our forwards. Alan Smith should be back by the end of August. He is a player we intend to convert back to centre-forward after a spell in the midfield last season," Ferguson said.
"We have Louis Saha and Wayne Rooney and there is the possibility we may keep Giuseppe Rossi if Van Nistelrooy does leave."
"It would be a consideration to keep Rossi at Old Trafford. I would prefer that he went on loan for six months anyway, so I have some good options," he added.
With interest in Atletico Madrid's Fernando Torres stalemating, Ferguson may begin the season with Saha and Rooney.
Though Ferguson has a well-developed back-up plan for forwards, his midfield is another matter. The Manchester United boss has confirmed his interest in Michael Carrick, but the club's initial offer was rejected by the Spurs.
"We are trying to sign another central midfielder," he said. "We have made a bid for Michael Carrick but they turned it down."