Italian insists the Manchester United man's frustrations did not lie with personal matters off the field, adding that the striker needs to learn from his 'mistake'
The Three Lions qualified after securing a point with a 2-2 draw in Montenegro despite throwing away a two-goal lead, and Rooney was sent off for needlessly kicking out at an opponent.
Despite his well-publicised off-field problems in the past week, Capello insisted that Rooney's actions can simply be put down to performance frustrations and that they lay only on the pitch.
"It surprised me. Right in front of me he kicked the opponent," the manager told Sky Sports.
"I think the red card came probably because he was not happy with the performance and when he lost the ball he kicked the opponent.
"But for the next game he will be suspended and we will try to find new solutions.
"He is an important player for us. Sometimes the important player doesn't play well and can make mistakes. It will be a good lesson for him, and also for the team.
"The player's frustrations are always on the pitch, not what happened away from here or private problems. He tried to do something.
"It was not easy to control the ball or play the ball because the pitch was not perfect and he wants to be the best always, and when you sometimes miss the ball, miss the passes, miss the control, he is unhappy for this reason. I figure he was frustrated."
The 69-year-old seemed relatively pleased despite the draw, commenting that qualification was the main goal for the team.
Capello added: "We are really happy. We played this game to qualify for the Euros, but I need to speak about the game because we played really well for most of it.
"After they scored, they found more chances to draw level - it completely changed the game. At the very end they drew the match and it is an OK result for both of us.
"I'm really happy with the game because to qualify was our first goal when we started the qualification for the Euros.
"The most important thing is to arrive at the goal. Sometimes you play well, sometimes not as well, but for 35 minutes in this game we played really well.
"I think in Bulgaria we also played really, really well, but it's not only this game we played well. Against Wales we played really well in the away game and in this match for the first half as well."
Capello then commented on England's next game, a friendly pencilled in with the world champions Spain at Wembley, and hinted that he will be picking a young team.
"Now we need to think about the next friendly game," he said.
"We will play against Spain at Wembley and I think for this game I will select young players.
"Some players will play for their first time in Wembley and it will be interesting."