Sorry to hear about you little guy, he's a cutie!
I agree with @ChickNanny13 I would try restricting activity for a few days if he's not too stressed and see if he improves. Keep him near the others. What I have done in the past too is confine most of the day, but let one out about an hour before roosting, let them roam a little and roost with the others. If it's injury, it can take a while for them to heal.
I would also give him 1/4 tablet B-Complex daily for a week or so, see if that makes a difference.
IF he does not improve with supportive care, something to think about would be Marek's.
I agree with @ChickNanny13 I would try restricting activity for a few days if he's not too stressed and see if he improves. Keep him near the others. What I have done in the past too is confine most of the day, but let one out about an hour before roosting, let them roam a little and roost with the others. If it's injury, it can take a while for them to heal.
I would also give him 1/4 tablet B-Complex daily for a week or so, see if that makes a difference.
IF he does not improve with supportive care, something to think about would be Marek's.