Second seed Andy Murray pulled out of the Dubai Championships Thursday with a virus.
The Briton had been due to play a quarter-final against Frenchman Richard Gasquet, who received a walkover.
"I got it the first time in Australia," Murray said of the illness. "I woke up in the middle of the night sweating. I got antibiotics from the doctor yesterday evening after the match and they obviously didn't help that much.
"I got up, had some breakfast and then slept again for three hours and then the guys woke me up and I wasn't feeling good."
Murray, whose participation in Britain's Davis Cup tie against Ukraine next week is now in doubt, said he had felt unwell between the sets of his second-round win over Arnaud Clement Wednesday.
"I felt really weak, and when the adrenalin wore off I felt very cold, sort of shivery. Obviously I've caught something, my temperature's up, sore throat, sore head, my body's aching a little bit, so I need to take some time off."
Murray said he was uncertain if he would be fit enough to play in Britain's Europe/Africa zone group one tie in Glasgow next week.
"I obviously want to try and play it," he said. "I'll see how I react to the antibiotics and give it my best shot to get ready.
"Doctor says I need a week, 10 days to start feeling better again, and you know, I'll just see. You never know with these things. Sometimes you can recover more quickly than other times."
Murray had to delay his return to Britain after becoming ill during the Australian Open but a medical check-up produced nothing significant.
"I had blood tests and stuff and none of them came back too bad but I was still on antibiotics for five or six days," said Murray, who later won his second title of the year in Rotterdam.
"I guess I started to feel a bit better towards the end of the week in Rotterdam. (But) it was really tough when you have a virus or whatever, you want to just spend time in bed, you're not feeling great."