Help my duckling is lame

[CanadianChix]

Hi all i has a muscovy duckling pass away and leave his sibling alone somi purchased some company two welsh harlequin x mallard ducklings and i just let them swim in the kiddie pool for a second time and now one of my welsh harlequin ducklings wont walk on his flippers he walks on the bones of his legs and has his flippers all curled in sideways like hook and he doesnt really wanna stand up he flippers stay all contracted it happened suddenly he was fine before no issues he is 3 weeks old a possible injury he doesn’t have any marks sores
Or visible malformations what could he have done I am baffled

 

[Miss Lydia]

Did he jump out of the pool onto hard ground?

 

[chickens really]

Definitely not good. A deficiency or spinal injury..