Leeds are anxiously waiting to discover the extent of Eirik Bakke's knee injury.
Bakke's injury has upset staff at Leeds
The midfielder has been diagnosed with patella tendonitis and has travelled to the United States to see a specialist knee surgeon.
There are fears that he could be ruled out for six months, which could prompt Leeds to seek compensation from the Norwegian Football Association.
Bakke, who sustained a knee injury during the latter half of last season, played for Norway in their Euro 2004 qualifiers against Denmark and Romania after being told to rest by the club's medical staff.
Bakke has since made just one brief appearance as a substitute against York during pre-season.
"It's disappointing for us and Eirik, but the problem now needs sorting out," said manager Peter Reid.
"I don't know how long he will be out for, but it's a big, big blow to us."
And Leeds physio Dave Hancock said: "He (Bakke) was advised to rest in the summer but by not doing this it has led to this problem now."
Bakke will also miss his country's crucial Euro 2004 qualifiers against Bosnia-Herzegovina and Luxembourg in September.