Beckham - omitted for Wednesday's game with Switzerland - told Sky Sports: "It's always disappointing when you're not included in an England squad.
"I haven't played since December so to be called up was probably unfair."
Capello's first match as manager of the England side is at Wembley but Beckham, who is only one appearance short of winning 100 caps, revealed he was not surprised by the decision to leave him out of the initial 30-man squad.
"I half expected it because I know what Fabio Capello is like as a manager," he added.
"If he thinks you're not fit and ready to play then you won't be in the team. I totally respect that and totally understand that.
"There are a lot of Premiership players who have played 15 games in the last two months and I haven't played a game since December."