Is this rude?

I’ve just accepted a new job and signed an offer letter. After telling my current employer that I’m leaving they’ve asked me to ask my new job if it is possibility to extend my new hire start date by one

Week so instead of starting in two weeks i would start in three. This would be to allow more time to train my replacement as my job is very hard to learn and two weeks wouldn’t be enough time since one week has already passed and the new girl starts today so one week to train isn’t enough time. Would this be a rude request or unprofessional to ask my new job? And if not how would I word it? Thanks everyone