I'd isolate this bird in a crate in the coop or run so it remains within sight of the flock.
If limp is really bothering them by inhibiting their normal activities too much, I will isolate them in a crate to 'force' rest for a day or two. Letting them out late in day, an hour before roost time, to give them a stretch and evaluate their mobility, then decide if they need another day and put them back in crate off roost after dark. Repeat stretch and eval the next day until they are better. Keep crate in coop so bird can remain 'with' the flock.
It may be dislocated or fractured rather than just a sprain...tho it can take many days for any improvement. Unless you can afford an xray you may just have to be patient.