It's possible but very unlikely. The onset of diabetes is usually signaled by three key symptoms: increased thirst, urination, and hunger. Numbness, pain, and tingling in the fingers and toes (neuropathy) are complications of long-term diabetes.
If your son is putting in a lot of training hours playing volleyball, he may be having a problem called de Quervain disease. Repeated motions and trauma to the base of the thumb are common in volleyball players. Inflammation of the thumb tendons can occur leading to de Quervain disease.
It's best to have him see a medical doctor for a proper diagnosis. This will put aside your fears and possibly nip the problem in the bud. Early detection for most conditions results in faster recovery and better outcomes.