France's double Olympic biathlon champion Martin Fourcade's season preparations have been hampered by glandular fever, the French Ski Federation (FFS) said on Tuesday.
The illness, which leaves the sufferer feeling extremely tired, could also hinder the 25-year-old's bid to compete in both the biathlon World Cup, which he has won for the past three seasons, and World Cup cross-country skiing events.
"Medical tests carried out recently as a result of Martin's extreme fatigue have revealed the presence of the virus," an FFS statement read.
"This illness has hampered his early season programme and forced Martin to rest for several weeks," it continued.
"His plans to contest simultaneously World Cup parallel skiing and the biathlon World Cup remain valid but the duration of his incapacity is unknown at this time," the statement concluded.
Fourcade won the 20km individual and 12.5km pursuit titles at the Winter Olympics in Sochi last February.
The World Cup gets underway in November.