King has a chronic knee problem that limits the amount of training he can take part in between matches.
The Tottenham defender has been sidelined with a thigh injury more recently but could return to the fold for Sunday's FA Cup semi-final against Portsmouth.
And his performances have been so impressive when he has been involved that Redknapp thinks he will get the nod from Fabio Capello.
The England coaching staff have remained in touch with Spurs and Redknapp feels King is so naturally fit that he would not let his country down.
"I still think he'll go to the World Cup," Redknapp said in the Sunday Mirror.
"If he's fit I think he'll go. Fabio often asks me how he is. The England coaches love Ledley. He's a fantastic player.
"He's desperate to be fit and available. When he played against Chelsea in the 2008 Carling Cup, that was his first game of that season and that went to extra-time.
"It's amazing how he does that. Not kicking a ball and then performing at that level. It's incredible."
Peter Crouch has also tipped his Tottenham team-mate to break into the England squad for the tournament in South Africa.
The striker said: "Who knows? If he plays every game towards the end of the season, then he's got a chance to go to the World Cup."