At least four other fans followed her onto the field, raising worries about security and underlining the concerns about the carnival-like atmosphere which has been created around the world champions in the small Swiss village.
Brazil's players had finished an attack-versus-defence practice and were doing stretching exercises on the ground when the incidents happened.
The blonde-haired woman jumped the fence around the field and appeared to land a kiss on the World Player of the Year Brazil striker Robinho jokingly threw a mattress over the pair.
Ronaldinho appeared to take it as a joke and even waved goodbye to the woman as she was led away.
A security official said that five people were arrested and taken away by police for questioning. He said that one appeared to be drunk and bit a policeman.
Brazil have been in Weggis since Monday to prepare for the World Cup finals where they face Croatia, Australia and Japan in their first-round group.
But instead of peace and quiet, their training sessions have been watched by around 5,000 people a day in a purpose built arena where the crowd is less than two metres from the pitch.
Practices have also been televised live in Brazil and scrutinised by around 800 journalists.
Coach Carlos Alberto Parreira, who initially said that training would be closed off if the crowd became too boisterous, said on Thursday the players enjoyed the carnival atmosphere.
