Help me with my new pet?

Hi I got seven 3 day old indian runner ducklings from efowl. One duckling was perfectly fine and running around but then he started limping and now he can still run but only for short seconds before having to lay down. I picked him up and I notice his foot is scrunched up. Is there anything I can do to fix this? Is it serious that he could die, I can't take him to the vet it's to pricey. Oh and all the other ducklings seem to be ignoring him, I feel bad for him. But does anyone have any ideas how to fix this? I'm very concerned. Please help and thank yu!