A deep lump inside the buttock cannot form a scab on the skin.The scab may be due to some other cause like infection,minor trauma getting healed.
There can be puckering on the skin due to deep lesion.
There can be lumps like Lipoma
etc in the buttock.
Nothing to worry.
Consult your Surgeon and get it removed.Send it for Histopathological examination(Biopsy
) and confirm the nature.
Benign tumours can occur in the buttock,which can turn into Malignant cancer in future.
Wish you good health