King, 30, has been at Spurs his entire career and is club captain - but he lives a strange existence for a professional footballer as he is unable to train regularly with team-mates.
The centre back was named among the substitutes for Tottenham's 0-0 Champions League draw with Milan and it was the first time he has featured in a matchday squad since October 16.
King has played just four games this season and has been suffering with a groin injury that Redknapp believes can be attributed to his restricted training regime.
"You have to train," Redknapp said. "You can't just come on Saturdays and expect to be the best player. Ledley has got away with not training all week and you can't do that for long. I think now he's finding it more difficult, as suddenly he's picked up a few more injuries.
"He's got a problem with his groin and we took a gamble with him [against Milan]. We just keep our fingers crossed for him and Jonathan Woodgate because they're fantastic centre halves. We're lucky that Michael Dawson has been brilliant and William Gallas has done a great job for us as well."
The doubts over King's long-term future and question marks that still remain over Woodgate's fitness mean that Redknapp will almost certainly dip into the transfer market for a top class centre back this summer.
Bolton centre-half Gary Cahill is a player Spurs have been linked with in the past and with a proven Premier League pedigree may represent a more favourable option than Redknapp's current alternatives - including Sebastien Basssong and January signing Bongani Khumalo - who have struggled to make an impact.
A less experienced option could be highly-rated Dinamo Zagreb star Sime Vrsaljko, with The Times claiming on Friday that Tottenham have already opened talks with the 19-year-old.
Dawson and Gallas have impressed as Spurs' first-choice centre-back partnership for much of the season and the Frenchman, who turns 34 in August, revealed on Thursday that he is hoping to be offered a new one-year deal at the end of the season.