The 25-year-old has expressed his wish to join rivals Chelsea, and it had been suggested that the figure could tempt Spurs to sell the Croatian international. However, Redknapp has stated that he values the player more highly than that.
"If we were looking to sell him it wouldn't meet my valuation," he said. "I think he is worth an awful lot more money than that."
However, the manager repeated his hope that the club won't sell the player.
"Really we're not looking to sell Luka. We need to keep our best players so he is a player that we want to keep if possible," he added.
The White Hart Lane club are currently in South Africa, where they face Orlando Pirates at Ellis Park tomorrow.