My gundog puppy is too scared to train after attack!
The trainer says he’ll get over it. Will he?
What has happened is that he has lost trust in your ability to protect him.
Your task is to re-establish that trust away from the training class and then re-introduce him to the class environment gradually.
Start by letting him stay in the car and watch.
The next stage is for him to be with you but a little way away from the class itself, until he is happy to join in again.
You could meanwhile arrange some one-to-one lessons with your trainer so that your dog can continue with his training, but without the pressure of having other dogs there.
Returning to group training has to be done in his time as his confidence returns, and cannot be rushed.
Ultimately, your dog will have to work with others, so this needs to be put right actively rather than just waiting for him to get over his fear, because some dogs will need more help with this than others.