A Surgical removal is the best bet to cure your pet and the procedure has a good chance of success because the abscess is on the flank. The most troublesome rabbit abscesses occur in the facial area.
PETBOOK magazine on MSN

11 common rabbit diseases

Rabbits, along with hamsters and guinea pigs, are among the most popular starter pets. However, these small animals have high care requirements and often suffer from illnesses that need treatment.