Mdtryhht

I am assigned as a reviewer of an article for IEEE TNNLS (computer science), but unfortunately, I would be super busy during the week of the deadline. In fact, I need to submit a paper and also two postdoc applications during the same week.

I'm already trying to do as much as I can before that week, but it'd make things much easier (with better quality) if I can postpone the review at least for two more days. So, I like to know if it looks unprofessional to ask the Editor for that extension and whether it'd damage my review performance/reputation in that journal?

Getting a review in two days late for a journal article is pretty common. I wouldn't worry about anything less than being a week late. For conferences, deadlines can be tighter, but 2 days is nothing. Ideally you would let the editor know your review will be a couple of days late, but even if you didn't, it is not the end of the world.

I wouldn't even ask. Just "tell".

Send a short email saying you will send the review a week later (more time than needed, don't want to come back in 2 days again). Don't phrase the email in a manner that requires a response from the editor--tell, don't ask (cut the back and forth chatter).

If the editor wants/needs to pull the paper, he will do so. But it's very unlikely he will. But just let him do what he does.

In addition, I would be practical and do a simple review. I love doing extensive murder board reviews. But you need to concentrate on your own stuff. There is probably an 80-20 rule where you can give 80% of the key improvements with 20% of the text and parsing time. In particular, if you are recommending rejection, I would be economical with your time and not investment much in improvement recommendations.