that is a little bigger than mine, but if it stays that size and doesn't get bigger so that the pump is sending air to the filter you are fine, I have a bubble about half that size unless I try to vacuum then it sucks air through a tiny leak and my pump basket empties and sucks air. you may have a pin hole or crack somewhere, it can be hard to find if the only way it leak is air on suction and not water out when theings are turned off. if you use hoses you can replace pretty easy. if hard plumbed you will have to really inspect every fitting.
is your pool an intex with the pressure relief fittings? I had to replace one of those once, it dripped and cause air to suck just a little as well.