Help!! My pet crow is limping :,(

Hi I have a baby carrion crow he is a great little lad. Eating and drinking well. But he has a problem, I'm not sure if it's life threatening or just a sprain, he's limping on his right leg. He puts the smallest amount of pressure on it but prefers to keep off it, he doesn't have much grip on it either. Should I be concerned? Please help! If this is bad can you recommend some treatments. I have read he could be low on vitamins D and A.

Thanks for looking!