United lose Anderson until February
The Brazilian is to see a specialist in Portugal for further assessment on the problem, having seen the same person two years ago following surgery for cruciate ligament damage.
"Anderson is out until February with a knee injury," Ferguson said. "He's been sent to Portugal to see a specialist who operated on him before. Not good news."
Ferguson is already without fellow midfielder Tom Cleverley, who is battling an ankle injury, but he will not be rushing into the transfer market come the January window.
"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," he said. "I do not see anyone who could make us a better team."
Ferguson also confirmed Wayne Rooney is back to fitness after he missed the Champions League game against Benfica having suffered a knock in last week's win at Swansea City.