Nottingham Forest's Carling Cup tie at home to Leicester was abandoned at half-time after Foxes defender Clive Clarke collapsed in the dressing room.
Paramedics rushed down the tunnel to attend to Clarke shortly after the half-time whistle.
A Leicester spokesman said the player was receiving medical attention in an ambulance and was conscious.
The restart was initially delayed before the referee called off the game, with Forest leading 1-0.
Forest boss Colin Calderwood and Leicester manager Martin Allen then emerged from the tunnel to make an announcement to the crowd.
Calderwood said: "We are afraid that due to the serious illness of a Leicester player both clubs have agreed to postpone the match."
The Reds held a 1-0 lead over their east midlands counterparts courtesy of Junior Agogo's 31st-minute strike.
