Dear Sir or Madam,
i am sorry to inform you that I am still recovering from the flu one month ago.I feel quite weak and dizzy,unable to focus on the work.Thus,I have to ask for three days' sick leave to have a thorough check-up at No.1 People's Hospital.
I hope that you could kindly consider my application and would highly appreciate your soonest approval.
many thanks.
Yours Sincerely,
xxx