Niki Lauda has been re-admitted to hospital in Vienna after contracting a flu infection during the festive break.
The three-time Formula 1 World Champion only recently left Austria's AKH Hospital, where he spent almost three months, following a lung transplant.
Lauda has been recovering at home since leaving hospital in late-October and although his recovery has been going well, he has since been vacant from the paddock.
His latest trip to hospital is believed to be precautionary, with the 69-year-old susceptible to infections due to a lower immune system as a result of major surgery.
Lauda's most recent communication was in November, when he issued a short video message thanking fans for their support, before revealing that Ferrari's Sebastian Vettel had sent him a handwritten letter whilst he was in hospital.
"As you all know I had a rough time from my health point of view and the support I got from all you people on my way was unbelievable," he said.
"The letter written by Sebastian, in his own hand, was a great pleasure for me, full of fine words and affectionate considerations. I didn't expect it, usually drivers don't do these things, they just drive. But he's a good person.
"He has had moments of discouragement, we know, but it would be absurd to question him. He will recover, a champion will not forget how to drive.
"He'll come back strong as ever and he'll still be [Lewis] Hamilton's rival in 2019."