He may need some motility med to keep him moving, I would call the vet to see if they can prescribe something for him. Keep pushing food under his face as much as possible to keep him eating.
How often and how much are you syringe feeding him? 3 or 4 times a day is ideal if he isn’t eating much on his own. I’ve found it helps to make the CC a little more runny than the package says, about the consistency of pancake batter. Go slowly, aim for the area behind the incisors, hopefully on the side that didn’t get injured. Squirt a little in, and wait for him to swallow. It’s normal for them to spit some out and for it to be messy, just keep at it. Mixing a little canned pumpkin in can make it more palatable for some bunnies. You can also try offering some on a plate. If he is hungry but his mouth just hurts, he might be happy to lick it up that way (some bunnies love it).
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.