Oleksandr Syrskyi.
International figures, including former US ambassador to Moscow Michael McFaul, had urged Zelenskyy to retain the minister.
Serhii Sternenko, an aide to Fedorov, expressed deep disappointment, pointing out that bureaucratic obstacles and delays hindered ongoing reforms.
He said the country had moved further away from victory as a result of the ouster.
Opposition politician Iryna Gerashchenko questioned the move in parliament, calling Fedorov the only sensible appointment made by Zelenskyy.
Public reaction online was critical, with thousands posting messages of support for Fedorov.
Artem Bronzhukov, deputy director of the Politika think tank, told Radio NV that rapid turnovers of defense ministers are abnormal during a large-scale war.
He emphasized that Fedorov had visibly enhanced the frontline situation in just a few months, turning Crimea into a virtual island and earning trust from progressive society and Western partners.
