Redknapp admitted he knew King was living on borrowed time last term.
Redknapp, who was sacked as Spurs manager last month, told The Sun: “Towards the end of the season he was struggling.
“We were struggling at centre-half with injuries and maybe we had one or two games too many.
“It was difficult for him in the end — he wasn’t the Ledley of the start of the year even. Because when he was at his best there was no doubt he was right up there with the best centre-halves you could find.”
Redknapp backed King to make a success of his new ambassadorial role.
He said: “There’s plenty of life left in him in terms of what he can offer the game.
“He is a top-class player and a special person and I was very lucky to have managed him late in his career.
“To have had him earlier when he was at his best, he would have been a world-class player.”