It could be a cover for the ethernet/network port. It also looks like the flap covering the optical audio port but that should not fall off because of the laser light coming out of the port when TV is powered. If the optical port is open, please put electric tape over it. At all cost, avoid looking directly at the port.
Hi there! Was this television purchased in the UK? That's the Conditional Access Module. It allows you access to some subscription services but it is not mandatory for the functionality of the TV. Here's a link with some additional information!
