The Brazilian midfielder, who had surgery after suffering cruciate ligament damage two years ago, has been sent back to the same specialist in Portugal for further assessment.
Anderson, 23, has not played since the Champions League clash with Otelul Galati on November 2 and the injury has turned out to be far worse than Alex Ferguson feared.
Fergie said: "Anderson is out until February with a knee injury.
"He's been sent to Portugal to see a specialist who operated on him before. It's not good news."
The blow throws Ferguson's midfield plans into chaos as Tom Cleverley is currently out of action with an ankle injury.
But the Scot, who was heavily linked with Luca Modric, Samir Nasri and Wesley Sneijder last summer, has no plans to go into the January transfer market.
He added: "It is easy to say you are going to buy players but it is not easy to buy them for Manchester United, especially in January.
"I do not see anyone who could make us a better team.
"There are two or three players but they are not available, so there is no point even going there."
Meanwhile, Ferguson has confirmed Wayne Rooney is fit for tomorrow's game with Newcastle at Old Trafford after missing the Champions League encounter against Benfica.
should sell this player
and buy other players