My cat's paw is much colder than normal. is this a circulation problem or an emergency? help please.?

our cat has 3 paws and his remaining hind paw is cold. he has cancer that caused the amputation of one hind paw, but today he has not been his normal self and his remaining hind paw is colder than normal. he is purring and is able to eat. he is not able to walk. our normal vet clinic can see him in the morning and he has a long medical history as he is 16 and i would rather wait to go there versus an emergency clinic if that does not creat unnecessary risk for our cat. help would be appreciated