A well-documented knee condition means that King is not able to train as normal with his team-mates.
The 30-year-old, who has not played for Spurs since October 16, was a surprise inclusion on the bench for Wednesday night's Champions League clash with AC Milan following a recent groin problem.
But Redknapp has suggested that the defender was not 100 per cent fit and that his recent setbacks are linked to his inability to maintain his overall fitness levels on the training field.
"He's got a problem with his groin and I'm not sure, really," the Spurs boss said. "I took a gamble with him on Wednesday night, but I don't know.
"He's got away with not training all week and playing on Saturday but I think it's starting to catch up on him now. You can't keep doing that for ever, you have to train.
"It's crazy that you can not train once all week and then come in on a Saturday and be the best player.
"Now he's finding it more difficult - suddenly he's starting to pick up a few more injures.
"We're just keeping our fingers crossed for him and Jonathan Woodgate, because they're two fantastic centre-halves.
"We're lucky that Michael Dawson has been brilliant and William Gallas has come in for us and done a great job for us as well."
