The Chelsea left-back has been sidelined since February after breaking his ankle and is facing a race against time to be fit for South Africa.
He has been pencilled in to return for Chelsea's home game with Stoke on April 25 and he will do so with Capello's words ringing in his ears.
"I know not all the players will be in the same shape. Some will have played the whole season, some will have played only half the season," he told Four Four Two magazine.
"If, for example, Ashley Cole is only half-fit, that's not enough. He needs to play too. After three months of being injured he will need games."
Capello went on to explain he is not a fan of playing players out of position and that he plans to use specialists at the World Cup.
Working on a marking system out of 10, the Italian concedes he has plenty of thinking to do before finalising his squad.
He added: "I think to myself: the value of this player is 10, another is nine, another is eight and a half. And I choose (the players with the) most (points).
"Everyone has different qualities. For some positions, one characteristic is more important than the other one.
"It depends on the position, it depends on different moments in the game, it depends on the opponents.
"I prefer the specialist. I think that 11 specialists win against 11 players who can play in different positions. It is nice to see players who can play in different positions though. There will be times when you have to do this."