The 18-year-old has already attracted the attentions of Wales boss John Toshack and became the youngest ever Bluebirds player to win a full international cap for Wales.
And, after receiving several bids from Tottenham, Cardiff revealed they had received an offer which had "reached their valuation" of the player.
The Bluebirds board had previously turned down two offers from Everton in the summer but chairman Peter Ridsdale admitted the latest offer from Spurs was too good for both parties to turn down.
"In our situation as a Championship football club, we have to consider anything of this magnitude," Ridsdale told the BBC.
"Chris has indicated he wants to talk to them and we have given permission.
"I think with the price itself we would have had to consider it no matter what the situation was financially."