Manchester United defender Gabriel Heinze will miss "most of the season" with cruciate knee ligament damage.
The 27-year-old Argentine was hurt in a tackle with Jan Kromkamp during the first half of United's Champions League tie with Villarreal in midweek.
Heinze's injury is a blow for United, who are set to be without Roy Keane for two weeks with a hamstring strain.
"It's not good news. He'll be out for most of the season. It's a bad blow," Ferguson told reporters on Friday.
He added: "It was one of those innocuous situations which you don't think anything serious will come from. But he landed awkwardly and that is what has done the damage."
The Argentine also faces a race against time to be fit for Argentina's World Cup campaign in Germany next year.
Gary Neville, Wes Brown, Louis Saha, Quinton Fortune and Ole Gunnar Solskjaer are also sidelined for United.
Kieran Richardson looks set to fill Heinze's left-back position in the Premiership game against Liverpool on Sunday.