Rooney experienced a second successive World Cup finals where he was below his best as England crashed out at the last 16 stage. Last week pictures emerged of the 24-year-old outside a Manchester nightclub, smoking and allegedly urinating behind a bin.
Capello heard of Rooney's antics before returning from holiday but will spell out the need to behave properly to the Manchester United star.
He said: "About Rooney, I read something in a Spanish paper and I read Alex Ferguson was not happy with this. I will speak with Rooney. They have to know they are really important people for the fans.
"I always speak with the players. They have to remember they are really important to the fans, and behaviour-wise we have to be careful. That applies to everyone. I will speak to Rooney when I meet him. I will remind him it is not good.''
Capello is aware several England players have been pictured in the newspapers enjoying their holidays following their exit from the World Cup. But he points out everyone has different ways of dealing with disappointment.
He said: "I think the reaction when you lose is different. Everyone has different reactions. I prefer to stay at home, others prefer to go out. Everyone chooses a different reaction.''
Capello has defended his decision not to attend the European Under-19 Championships in which England reached the semi-finals. But he opted to watch the games on television after being told none of the players were yet ready for a call into the senior set-up.
Capello said: "Before I decided to go, I spoke with Franco Baldini, Stuart Pearce, Ray Clemence and the coaches. I spoke with Trevor Brooking to see if some players were really interesting to check and monitor. He told me no one was ready for the senior team. For this reason I watched all the games on TV and I stayed with my family.''
Capello also confirmed he will look to add another English coach into the set-up.
He said: "I've big confidence in Stuart and Ray. They did a great job in South Africa. We will speak with Trevor Brooking about what we can do in the future (regarding another coach).''