How is he doing?
Over the years I have had many squabs scalped and injured by adult male pigeons.
Don't worry about the blood and missing feathers. They heal superfast and the feathers re grown quickly too. My worst case was a squab which had be scalped very badly, even thought it lost an eye.. and just the skull showing on its head. It got a huge scab over its head and I was really worried it would die. However, it recovered within a couple of weeks so here was no way to tell anything had happened. They are growing so fast at this age they also heal faster too.
But in your squabs case, I fear it may have injured itself internally from the fall, rather then the males pecking it.
Shut off its next box with its parents in there with it... and food and water for them all. Let the parents take care of it... let it rest and recover from the ordeal.
If the next day and its crop is empty, please force feed it a mixture of liquid hand rearing formula, or chicken food mixed with water to be a paste. You can get tips off the internet about how to do this.
I personally found the easiest was to put the warm mix in a plastic bag and cut a corner off the bag just big enough to push the squabs beak through into the mix. It should automatically begin gulping down the mix once its beak is in it. If it need a breath it will pull its beak out.
Wishing you luck!