Police are investigating after the allegations were made about the England full-back in a national newspaper.
City manager Guardiola told reporters on Friday it was a "private issue".
"We solved it internally, speaking with him. Of course this is not the place to discuss private situations," he said.
The incident is alleged to have taken place during a two-day break after City's Premier League victory over Newcastle last week.
It is understood Walker contests the allegations and has reported for training as normal this week.
On the general issue of the importance of players being careful about their behaviour in public, Guardiola said: "It's completely different from years ago. They know it.
"When you open the door at home you have to know you will be filmed whatever you do. It is part of society."
City, who travel to face Crystal Palace on Saturday, are currently second in the Premier League, five points behind leaders Arsenal.
