If you carefully dig it up you can check the roots, they look nothing like a daylily. Nutsedge has a tiny tubor like Tink said that you must remove or it will grow back. If it really looks like a daylily then you could replant it in a pot to keep an eye on it.
Picture below from here:http://sadlerhoa.wordpress.com/2012/06/29/your-lawn-will-survive/
