Playing football Demchenko started out in his native
Zaporizhzhia where his first coach (trainer) was Borys Zozulya and Viktor Vysochyn. When Demchenko turned 13, his new trainer was Anatoliy Vasyleha who coached him before Demchenko moved to Moscow. During his teenage years Demchenko was spotted by
Gennadiy Kostylev, a
Soviet Union national team coach, and Demchenko participated in some international tournaments among junior teams. During
dissolution of the Soviet Union, in 1990 Demchenko was invited as a prospect player to play for
PFC CSKA Moscow where Kostylev also became the club's manager. At the 1994 European U-18 Championship Demchenko, playing for the
Russia national team, became a top scorer of the tournament. At that tournament played such football personalities like
Raúl,
Fernando Morientes,
Míchel Salgado,
Lars Ricken,
Francesco Totti and others. Following the European championship
Ajax offered $1 million Moscow team for the 17-year-old Demchenko and both player and club agreed. At Ajax, Demchenko mostly sat on the bench and had limited amount of playing experience. Following end of contract with the Dutch club, he returned to
Zaporizhzhia where he joined
Metalurh Zaporizhzhia. == Managerial career ==