Foot drop is caused by damage to

The common peroneal nerve is a component of the sciatic nerve. In the posterior thigh, it supplies the sho head of biceps femoris. It curves around neck of fibula deep to peroneus longus and divides into superficial and deep peroneal nerves. The superficial peroneal nerve innervates peroneus longus and peroneus brevis which are the eveors of foot and to the skin over the dorsal area of foot except the first webspace and lateral side of little toe. The deep peroneal nerve innervates all muscles of anterior compa which are the dorsiflexors of foot, extensor digitorum brevis, first two dorsal interossei muscles and skin between great and second toes. Hence, injury to common peroneal nerve will lead to weakness of dorsiflexion of foot or foot drop, loss of eversion, loss of extension of toes and sensory loss along anterior and lateral side of leg, dorsum of foot including medial side of great toe. Ref: Gray&;s Anatomy 41st edition PGno: 632