How did he get hurt? Was it something that happened in the other barn?
Perhaps he is afraid that it will happen again.
Do you know the people where you are boarding now? Sometimes the surroundings are not always ideal.
Smart Calm is a good suggestion from Smartpak. It helps my 8 yr. old Tennessee Walker.
Whatever you do spend more time with him so that he feels more comfortable and you can monitor how they do things at the barn.