Mouth-to-mouth resuscitation attempts failed and paramedics needed to use a defibrilator to get him breathing again.
The left-back was taken to the Queens Medical Centre in Nottingham, where he remains in their cardiac unit.
"It appears Clive's heart stopped twice, mouth-to-mouth didn't work so the paramedics had to use a defibrilator," said the player's agent Gary Mellor.
"He is sitting up and talking, and is going to have more tests on Wednesday afternoon.
"His family are very upset, especially after what happened with the Sevilla player Antonio Puerta dying recently. We just hope he is going to be okay."
The Carling Cup second round tie was abandoned and will be replayed at a later date.
