Crouch has known of King's qualities for more than a decade since his first spell at Tottenham as a schoolboy.
And the striker has seen at first hand King's impact at White Hart Lane since returning to the club for a second spell.
King is part of Fabio Capello's provisional squad of 30 for South Africa and is likely to be named in the final 23.
Crouch believes he will be a key figure if he stays clear of the knee problem which has blighted his career.
Crouch said: "Ledley has been brilliant. I've known Ledley for a lot of years and I know what a superb player he is. I've known Ledley since I was 13 in my first spell at Spurs. He was fantastic even then. Even then you knew he was going to be world class and he has proven that.
"As long as he can prove his fitness, he will be up there as one of the best centre-halfs at the World Cup. He has proved his quality this season, hopefully he has proved his fitness. He played the last three games of the season, all for the 90 minutes, he came through those and trained this week with England as well."
Crouch added: "It is a big boost because he is such a quality player and everyone would be happy to have him in their squad. Ledley has to be managed a bit different to the rest of the players. He has to do his own thing and train when he feels capable of it. Without a doubt, the manager thinks it is worthwhile him coming and, on his day when he is fit, there are not many as good as him."
Crouch has also welcomed the recall to the squad of another centre-back in Jamie Carragher, whom he played alongside during his spell at Liverpool.
He said: "Jamie brings a great deal of experience. He has played at top level for a long, long time now. I played with Jamie for three years at Liverpool and he is a leader and has great experience - and having that experience at major tournaments certainly helps."