Manchester United full-back Gabriel Heinze will miss most of the season after a scan revealed serious knee ligament damage, manager Alex Ferguson said yesterday.

The Argentina left-back was carried off after half an hour of United's goalless draw with Villarreal in the Champions League on Wednesday.

"It's not good news. He's going to be out for most of the season. He's got a cruciate injury. It's a bad blow," Ferguson told reporters.

"It was an innocuous incident but I think it was the way he landed which did the damage."

The 27-year-old's energetic displays earned him the fans' player of the year award last season while his absence will also be keenly missed by Argentina, although they have already qualified for next year's World Cup.

United are currently without captain Roy Keane (hamstring) and strikers Louis Saha and Ole Gunnar Solskjaer, both with knee injuries.

But it is in defence where Ferguson's major problems now lie with Gary Neville (groin), Wes Brown (thigh) and Quinton Fortune (knee) all injured.

"Quinton can play in several positions but you are talking about four players who are capable of playing in defensive positions, and that it is a concern and one I hope starts to get better in the next couple of weeks," Ferguson said.

Fellow defender Rio Ferdinand said of Heinze's latest setback: "It's a massive blow. He's been an integral part of the team since he arrived. He was a fantastic addition to the squad, both on and off the pitch.

Kieran Richardson, who replaced Heinze in Spain and has impressed Ferguson since returning from a loan spell at West Bromwich Albion last season, is likely to step into the role on a regular basis, beginning at Liverpool tomorrow.