It is surely a thing to worry and to be looked into.
As he is a Topper he can definitely complete his studies through alternate arrangements.
Yet , to know about the issue behind it is also important .
Something which has happened in his school or as such the system of schooling itself is suddenly not acceptable to him
Next Steps
Try to visit a Psychologist in your city and give him.the space and confidence to share his feelings to them.
He might get a clarity to how to proceed .