Hi there...
There is an autoimmune condition known as Pemphigus. I don't know much about it, except that Greyhounds are prone to it, and...
This condition affects the toenails of the dog.
It sounds like your dog may have this....so you might want to do some internet research on the subject. ( I hope that he only has split nails...! )
Good Luck and best wishes for you and your dog.
Connie
If you can't take him to the vet, start soaking the paw in warm epson salt water every day, twice a day. If you don't have epson salts, regular salt will work okay. You can wash the paw with mild soapy water before soaking. If it doesn't improve in a week, take him to the vet.
Maybe he has something stuck in his paw or maybe he has something worst...if he's limping you should take him to the vet to make sure it's trated right away and maybe avoid an nasty infection!