King said that she had tipped Robson, winner of the 2008 Wimbledon junior title at 14, as the best youngster in her age group but belief that she can beat the world's top players is essential.
"Having a win over Kim Clijsters will help her self-confidence and that's what she needs the most," Sky Sports News quotes King as saying.
"Laura needs to believe in herself and her abilities, believe the ball is going in. Beating a player of Clijsters's ability and stature is really going to help her.
"I saw her junior final at Wimbledon and thought that this is the girl that is the best of the kids coming up. You have to be older now to make the transition and become a top player so it takes time."
Robson faces Li Na later on today in the third round of the US Open.