From world leaders to celebrities of all degrees of fame, taking a selfie with fans has become an accepted part of life.

But tennis great Roger Federer felt an unacceptable line was crossed Sunday when a spectator invaded center court at the French Open to try to get a snap with the 17-time grand slam winner.

The boy -- reportedly a teenager -- got close enough to Federer to put his arms around his shoulders as he was walking off the playing arena.

It raised fears over security in a city where just a few months ago terrorists killed 11 people in the offices of satirical magazine Charlie Hebdo.

The incident also brought back memories of the 1993 attack on former women's No. 1 Monica Seles, who quit playing for two years after being stabbed during a tournament in Germany.

"I'm not happy about it -- obviously not for one second am I happy about it," Federer told reporters after winning his opening match on day one at Roland Garros.

"It happened yesterday in the practice, too. It's just a kid, but then three more kids came.

"And today on center court where you would think this is a place where nobody can come on, he just wanders on and nothing happens."

For Federer, it brought back memories of 2009 when a fan in Swiss colors tried to put a flag on his head during the French Open final against Robin Soderling -- which he won for his only grand slam triumph on clay.

"I definitely think something needs to happen quickly," said the 33-year-old.