According to a report in the Daily Mirror, Redknapp was asked about a £10m release clause in the Senegalese striker's contract.
“I think you will find it is a lot less than that.”
Asked if was as little as £7m, Redknapp added: “Even less than that.”
Redknapp is now likely to make a move for Ba, who only joined Newcastle from West Ham in the summer.
The forward has been prolific so far this season, scoring 15 goals.
He has blown away fears of a serious knee injury that prompted Stoke to pull out of a transfer for Ba last January.
Should he move in this month, it would mean he will have played for 4 different clubs in just 2 seasons