Dear
This is in the reference to the letter received dated (date) We would like to inform you that Mr. Smith is out of the office for the next two weeks on sick leave. I am acknowledging receipt of your letter dated (date). I assure you that it will be brought to his attention immediately upon his return and he will get back to you on the same regarding it.
If I may be of any assistance during Mr. Smith absence, please feel free to call us.