The port does not get shut down, it either works or it does not.
Have the following been tried:
Replace Ethernet cable?
Different Ethernet port on the router or switch?
If those do not resolve the issue and a restart and restore of the ATV does not resolve the issue then the port has likely failed. Take the device to Apple for evaluation and possible replacement.
Hello Diesel vdub
Thanks very much for answering me so quickly and your suggestions. We have two ATV 2nd Gen boxes that connect to the switch via Devolo DLAN boxes which have worked virtually flawlessly in both the living room and bedroom for just over a year now. It was last week that the living room ATV box decided to go on its wifi connection, I swapped the ATV boxes over and the fault followed the ATV, therefore as you suggest it is most probably the ATV itself. Great, just out of warranty too, thank you, Apple.