Paris: Losing Lassana Diarra for the World Cup is a "hard blow" for France, coach Raymond Domenech said on Sunday.
Midfielder Diarra, who left the team on Saturday after missing training for three days because of persistent stomach pains, has been ruled out of the June 11-July 11 finals in South Africa.
The 25-year-old, who has won 27 caps for France, suffers from a genetic blood disorder affecting red blood cells and causing chronic fatigue, his Real Madrid club said in a statement.
The player, who started feeling unwell on a hike up a glacier in the French Alps resort of Tignes, where France are in a week-long training camp, will have to rest for an indeterminate period, a France team spokesman said.
"It`s a hard blow for him, because he had worked very hard to be at the World Cup, and for us, because he was an important member of that team with his playing style and mental strength," Domenech said in a video posted on the French Football Federation`s website.
On Thursday, the first day he could not train, Diarra, whose illness might have been aggravated by altitude, was seen talking to Domenech for 45 minutes during the session.
The coach, who had taken a provisional 24-man squad to Tignes, has not yet decided whether Diarra would be replaced.
"It`s difficult to tell, when you lose a player, if you are going to take another one," Domenech said. "We have few days to make a decision, we will see."
Domenech, who has until Tuesday to name his final 23-man squad, had picked 24 players because of a question mark over the fitness of William Gallas.
Centre back Gallas, who suffered a recurrence of a left calf muscle injury in late March and has not played since, completed Saturday`s 90-minute session raising hopes he would be fit for the World Cup.
France face the hosts South Africa, Mexico and Uruguay in Group A.