It appears to be fluid from a systemic infection. How old is this chick? Do you see any swelling of the leg joints? How about cuts or bruising or scabs? Look at the bottom of the feet, too.
Pain is probably involved so a quarter of a baby aspirin twice a day can help.
You need to soak the legs and feet in very warm water with Betadine and Epsom salt twice a day. If the condition worsens or doesn't improve after three days, you will probably need to administer a round of an antibiotic such as amoxicillin.
There's a chance this is being caused by an infectious virus. The antibiotic may not help except for secondary infection.