It is been a few days since your message.
How is the bird doing now?
If there are no visible signs I can think of two things:
1) The bird is hurt internaly. Maybe has a bne or something cracked.
Hopefully, it is nothing serious.
If he is still looking OK, give it some time and don't push him.
2) It is scared.
This is very normal and happens frequently.
Again, don't push him. Let him gain his confidance.
Let him in and out of the loft with the other birds but don't push him to fly.
If he has been flying sooner or later he will show you he is ready to go up again.
Very rare but every once in a while you will get a bird that is so scared it will never recover and want to fly.
I have not had success with a bird like that.
Maybe some one else who has a positive experience will share with us.