Question regarding Tenser's Floating Disk and Telekinesis

What would happen if a character would sit on a Tensers Floating Disk and using Telekinesis raise the wizard who the disk is following 40ft away from the disk...and keep him 40ft away at all time?

Would they travel at bullet speed or some other way?

I imagine the disk would instantly slip put under the caster or there would be a Dex save or something...