The fourth Test between India and England required a change of umpire on Thursday after Paul Reiffel was struck on the back of the head by a wayward throw.
Umpire Reiffel was caught unaware at square-leg as Bhuvneshwar Kumar lobbed the ball in his direction from the deep, and the former Australia international fell to the ground upon impact.
England's medical staff rushed to the shaken official's aid and Reiffel was subsequently escorted from the field for further assessment.
Marais Erasmus, the third umpire, walked out to replace Reiffel after a short delay, with England 166-2 after 48.2 overs in Mumbai.
Reiffel is thought to have travelled to hospital for a scan on the injury.