Tort of Negligence in Medical Negligence

Rohan, a 25-yr-old software engineer, undergoes a minor surgery for appendicitis at City Hospital, run by Dr. Singh and his team. During surgery, Dr. Singh negligently leaves a surgical instrument inside Rohan's abdomen. Two months later, Rohan develops severe abdominal pain and a fever. An MRI reveals the presence of the instrument, which has caused a severe infection. As a result, Rohan suffers from long-term liver damage and requires costly treatment. What legal remedy can Rohan claim against Dr. Singh and City Hospital for their negligence?