The Italian saw Wilshere, who has only made one substitute appearance in the Premier League, star in the pre-season Emirates Cup tournament, scoring twice against Rangers.
And Capello said of the 17-year-old: "He surprised me. Really. I saw him last year two times because he played in the Carling Cup and he has improved a lot now.
"He plays without fear, with confidence. And the other players passed the ball always to him. This is not normal to be so young and so good."
Sven-Goran Eriksson took another Arsenal youngster, Theo Walcott, to the World Cup finals in 2006 before he had played in the Premier League but Capello stressed Wilshere must break into the first team if he is to earn a place in the squad.
He continued: "We have time before we have to decide if he will go to South Africa. It depends a lot on (Gunners boss) Arsene Wenger, if he will play him."
Meanwhile, Michael Owen intends to keep his head down and continue battling to win back his England place.
"I've been in the provisional squad quite a few times but the final squad is the one you want to be in," the Manchester United striker said.
"I have had a good start to my United career. I haven't missed a training session or a match.
"But it's down to the management. I have just got to continue doing well and see where that takes me."
It could be argued the opposition the United striker faced in the Far East, when he scored all his goals so far, was not exactly the strongest.
However, as the former Liverpool star pointed out, you can only score against the defenders put in front of you and he is confident once the Premier League champions tackle Birmingham at Old Trafford, he will continue in the same vein.
"I have done as well as I can in pre-season, now I am just eager to start the new season like anyone else," he said.
"It has been easy to settle in at United. The players have made me very welcome and I feel like I have been here a couple of years already.
"Now I just want the season to start."