Won't affect it at all. It's perfectly fine so long as that panel remains in place. It's microwaves. It works by directing microwaves from an emitter into the interior and exciting/vibrating the water molecules in food items, which imparts thermal energy, more or less. The housing of the microwaves is plenty of shielding from the emitter and than panel probably does little more than provide a surface that is easy to clean and won't melt if something is overheated in the microwave.