Upvote:1
There is a possibility you will have to pay, as I am reading on TripAdvisor they are very strict on bags:
Etihad is extremely strict at check in on carry on baggage size, it's weight, and also the weight of checked baggage, so much so that at Abu Dhabi there are scales and areas for passengers to re-distribute contents across bags to balance weight variations.
Also, from this question:
Airlines do weigh checked baggage and that is the most important measurement, actual dimensions are almost never measured for 'normal' luggage. Even when they do, small differences are hardly ever a problem, especially if the overall dimensions are good. There is, however, no guaranty a specific agent may measure and give you a harder time. At this time there is no tradition of measuring luggage out of sight of the passenger and coming back to them with complains.
If the rules change in the future, you might be stuck with a piece of luggage that can not be used on flights.