East Bengal F.C.
Zelený made his debut for Mohun Bagan A.C. in the East Bengal derby against Kingfisher East Bengal F.C. in front of 100 000 spectators. Zelený received widespread praise for his good performance in his first game for Mohun Bagan A.C., and would remain as a cult figure against Kingfisher East Bengal F.C. for the remainder of his tenure at Mohun Bagan A.C., earning the moniker of "Mr. Derby" amongst the supporters for his impressive performances against fiercest rivals Kingfisher East Bengal F.C.