Barton, 28, spoke of his belief last season that he was the best English central midfielder.
However, Capello believes that Barton's lack of discipline renders him too great a risk for selection.
"I think Joey Barton is a good player but he is a dangerous player because sometimes on the pitch you can play 10 versus 11 because he might get sent off," Capello told The Mirror.
"That is the problem you face with him."
Newcastle United recently told Barton that he is free to find another club after he made negative comments about the board on Twitter.