Hi
It sounds to me like your cat was bitten by another cat. The small hard lump of fur was likely to have been a scab over the wound. If there's any swelling or the discharge gets heavier it is likely to be developing into an infected abscess. Sometimes bite wounds heal but they often become infected due to bacteria that are on the attacking cat's teeth getting implanted into the wound. If your cat becomes unwell with any swelling, pain or a discharge from the wound then do take him to your vet for treatment.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]