I am writing to inform you that I may not be able to attend office for a week from now i.e., from (give duration), as I am suffering from flu. I have been advised by the doctor to take bed rest for faster recovery. I regret the inconvenience caused because of my illness.
I am willing to put in extra efforts to reimburse the delay at work once I am back from my leave.(or I would try my level best to resume my duty as early as possible)
Thanks and regards,