Chelsea target Michael Essien has dropped out of the Lyon squad for their opening Ligue 1 game against Le Mans on Sunday with a stomach complaint.
Essien has won two French titles with Lyon
A statement on the French champions' website said the 22-year-old had lost 2kg in weight because of his condition.
Lyon coach Gerard Houllier said he was unsure when Essien would return.
The club are believed to have rejected a Chelsea bid in excess of £21m for Essien, and are holding out for £32m fee as well as a player in exchange.
Essien did not feature in Wednesday's 4-1 victory over Auxerre in the Trophy of Champions..
The midfielder has said he wants to join Chelsea and is "convinced" it will happen.
Lyon chairman Jean-Michel Aulas and Blues owner Roman Abramovich are due to meet in France next week to discuss Essien.
Essien has been a revelation for the French champions since signing from Bastia two years ago, helping them win two Ligue 1 titles.
Lyon have won the Ligue 1 championship for the last four years.