Jun.24 (GMM) Timo Glock will almost certainly sit out Sunday's European Grand Prix.
The German sat out qualifying on Saturday, and according to multiple media sources he was travelling to a local hospital for checks whilst his usual rivals were in action on the Valencia street circuit.
Marussia has described the 30-year-old's ailment as a "stomach bug", but sources say he could be suffering from either food poisoning or a virus.
Bild newspaper said he will "almost certainly" not race on Sunday, even though the FIA has said that despite him missing qualifying, he will be allowed to compete subject to a medical green light.
But the German publication said doctors have in fact advised Glock to sit out Valencia, particularly as over the past few days, his body has been unable to retain many fluids.
Sunday in the Spanish port city is expected to be hot and dry.
Marussia's test driver Maria de Villota does not have a mandatory FIA super license.
Red Bull reserve Sebastien Buemi told Auto Motor und Sport he offered to race in Glock's place, but Marussia will in fact contest the European Grand Prix with only one car in the event Glock is not fit to return.
"Our objective for Sunday's race, whatever it may hold, will simply be to do the best job possible in the circumstances," said team boss John Booth.