A letter to my manager

Dear manager:

I'm regret to inform you that I cannot(when writing more formal letters, it's best to keep contractions out) come to work for a while starting *next week. As you know, my wife has been pregnant for several months. Her doctor told us today that she needs to stay in the hospital until she gives birth. I'm not sure by what time I can come back at the moment,but at least for next week, I will not be able to show myself at the office, if you approve my application. During my time off, John can help with the work, as he has been my assistant for half a year.

Yours sincerely,

Hunter

*This sentence's wording is a little off, if you're going to need next week off- I would say "I cannot come to work starting next week for (insert amount of time you'll need to be gone, for example:) two weeks." I think that's what you meant! 

Also, good luck with your wife and life as a new father!