The Chelsea star said: “You get high points and low points in your life.
“In addition, when I arrived I was tired from playing at the World Cup.
“And, right now, I feel really bad. I have been in bed with a high fever that has reached 39.4 degrees and even speaking is painful for me.
“The doctors told me I have picked up a viral infection. I began having problems on Tuesday, when I arrived in Kiev for the Ukraine team’s get-together.
“I don’t yet know whether I will miss the game against Italy, as the doctors won’t commit themselves, but my fever has continued to rise.”
The £30million summer signing from AC Milan, has just scored twice in English football so far this season.