The Scot warned that the 28-year-old, who has never been beyond the last eight of a Grand Slam, is capable of producing a shock if he truly believes in himself.
"If someone goes on the court not thinking they can win against you, then the match is as good as done," Reuters quotes the 26-year-old as saying.
"When they believe they can win, in an individual sport when you're just playing against one person, then you can cause an upset. It's as simple as that.
"Stan has improved quite a bit this year. He hasn't changed any of his strokes, technically. You'd expect most of it to be confidence."