"I can never see any real diamonds in January, only now and again," Ferguson told a news conference on Friday.
"It is still the case that I won't be buying."
Ferguson said the Premier League club's widely-publicised mounting debt had not affected his spending power.
Media reports this week said the Glazer family, the American leisure tycoons who bought United in 2005, were looking at ways of easing the club's debt burden.
"We have got the money. There is no doubt about that, no question," said Ferguson.
"I just don't see that player who can make a difference for us in terms of value and availability.
"We struck lucky with (Nemanja) Vidic and (Patrice) Evra, although it took them time to adjust. We bought (Louis) Saha in the window, who was a marvellous player but had a lot of injuries. And we bought Andy Cole in the window, who was fantastic.
"So those have been success stories for us but you can't guarantee that in January. You're looking for players to possibly play in Europe and that's limited because of other teams' involvement in Europe. It's never a certain success route."
United, who travel to Birmingham City on Saturday, are second in the Premier League, two points behind Chelsea.
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