Ardiles, who won the 1978 World Cup with Argentina, believes Capello will spring a major shock when he announces his squad for South Africa - and Beckham might be that shock.
Beckham has agreed to move to AC Milan on loan from LA Galaxy in order to keep fit and ensure he is ready to make history as the only Englishman ever to play in four successive World Cup finals.
But Ardiles, who wants England to win if his own country cannot, says Beckham could be a surprise omission from Capello's final squad selection.
In an exclusive World Cup column for ESPN Soccernet, Ardiles said: "The fact that Capello is in charge means you can be assured that he will select the right balance in his squad, and he will make sure he gets his selection spot on. If that means leaving out David Beckham, that is what he will do.
"In fact, there is more competition for places on the right side of midfield than anywhere else in the team. Capello has dynamic young players such as Theo Walcott, Aaron Lennon, Shaun Wright-Phillips and James Milner, so I don't think Beckham is a certainty.
"I think that Lennon is a certainty, and Capello has been careful not to say anything to suggest that Beckham is definitely going. People have assumed Beckham is a certainty but, if you listen to Capello carefully, he has not said Beckham will definitely go. Let's wait and see. There could be a major surprise from Mr Capello, and there will be a big surprise for many if Beckham doesn't go, and I could see that happening."
Ardiles has also revealed that he could see Cristiano Ronaldo facing an early exit after Portugal were placed in a group with Brazil, Ivory Coast and North Korea.
"Of course, Brazil's group is always going to be eye-catching, and there is no doubt that Ivory Coast are the best team in Africa," he said. "Portugal are a great team on their day, but they are not reliable.
"For that reason, I predict that Portugal and Cristiano Ronaldo will be going home early, with Brazil and Ivory Coast going through. If Ronaldo does go out early, so be it - that's the way the game can go sometimes."