I never recommend placing potted plants directly on hardwood even if you put plastic, or some sort of water catcher underneath.  Instead you should use some sort of plant stand or trivet to raise it off the ground and let air circulate underneath to avoid condensation building up. I would use a saucer of some sort underneath to catch water from dripped as well as a short stand.

If you disregard that advice, use a plastic saucer sitting on a cloth so that it does not scratch your hardwood.