Duckling cannot walk, dragging one leg behind him, please help!

[Ephyra]

(Not my duckling, posting for someone else)

He's 13 days old, it began a couple days ago. Her vet won't see him unless it's a broken leg... There's no swelling and does not appear to be painful, but he cannot walk. He falls on his face and drags the leg behind him. He appears to be in good health otherwise. His diet is duck starter/grower. Any ideas? Thanks so much for any help!

Video of him trying to walk:

 

[Stipenvlerk]

Hi @Ephyra
Sorry no one answered earlier...
I think it would not hurt to rule our Niacin deficiency:
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/
Meanwhile I tagg some experts : @Isaac 0 @Miss Lydia

Please update how the little one is doing!

 

[Miss Lydia]

Possibly an injury or niacin deficiency but I'd say injury since usually niacin def is both legs. But rest warm water therapy and liquid B compex can help. Is this the only duckling? was it with it's mama? Just wondering if it may have gotten stepped on? Jumped off a ledge etc? Warm water therapy is just letting the little one float in warm water taking pressue off the leg but hopefully getting it to start moving it to help keep muscles working and aids in healing. B complex is so good for them if a niacin deficiency.
https://www.backyardchickens.com/threads/niacin-deficiency-in-waterfowl.1367557/