Exemption on medical ground

Namaste Dear Experts, In the present case, PW has agreed for voice sample. In the Defence witness accused has filed application for voice sample as a defence witness. This application was allowed by ACJM. After multiple summons and warrants, now witness has filed application that he cannot go for voice sample because he got stones in both the kidney hence he cannot travel. It is matter of fact that he is govt. Lecturer and doing duty in time. How can we enforce him for voice sample and what are alternates for us if judge accept his application. Whether same judge has power to decide application against his own decision.