It looks kind of like a water sucker. Musa reproduce vegetatively from corms that form mats under the soil. I actually do not think your plant is potted deeply enough. When they produce suckers, they make 2 basic kinds....water suckers, and sword suckers. Sword suckers are tall and fast growing with very narrow leaves. They are the plants that 'carry on' the stand after the mother plant fruits and died. Water suckers and smaller slower growing and have wider leaves. Their purpose is to help expand the stand and make a colony but at a slower rate.
If your banana had been planted a little deeper, the sucker would have eventually made its own roots. As it is now, it is dependent on the roots of the mother.
You can leave it, or, you can take it off and try potting it up. It might grow on its own and it may eventually produce a sword sucker, or it might not.
