Alonso on antibiotics to tackle fever
The Spaniard limited his track time and was unusually outpaced by his teammate Nelson Piquet during Friday's three hours of practice, having curtailed his activities at the track the day before with an ear infection.
Alonso, 27, said he felt better on Friday that he did 24 hours ago.
Spain's Diario AS said he is taking antibiotics to tackle his high temperature.
"Hopefully I will recover more this evening and feel better tomorrow so I can give my maximum for qualifying which I think will be one of the most important parts of the weekend," he said.
Worsening matters, the oppressive heat and humidity makes Malaysia one of the toughest races physically on the entire F1 calendar, but Alonso insists he could not have simply sat out Friday's action altogether.
"It's a very demanding weekend in terms of the heat because we sweat so much but it was important we still got enough information," he said.