Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
"Saddened by all that is occurring in Brazil," Neymar wrote in a statement issued hours before Brazil was to face off against Mexico in their second Confederations Cup match in the northeastern city of Fortaleza.
"I always had faith that it would not be necessary to come to the point of having to take to the streets to demand better conditions for transport, health, education and security," he noted.
"All this is the OBLIGATION of the government," he wrote.
Brazil has been rocked this week by the biggest protests in 20 years over the $15 billion being invested in the Confederations Cup and next year´s World Cup while education and health are underfunded.
The demonstrators have also been railing against higher mass transit fares and a political class widely viewed as corrupt.
Neymar stressed that he wanted a country that is "more just, safer, healthier and more honest."
He said he and his teammates would be inspired by the mass protests when they play against Mexico later in the day.
On Tuesday, teammate David Luiz also spoke out in support of the mass protests, saying: "I'm in favor of demonstrations without violence."
"Citizens have a right to express their opinions and the fact they're not happy. It's a way of achieving their demands and improving the situation in the country."
Dani Alves, another Selecao player, also gave his backing.
On his Instagram online photo-sharing account, he posted a picture of a human eye made to resemble the yellow and green national flag, with the motto "Order and Progress" written across the pupil.
"Order and Progress without violence for a better Brazil, a peaceful Brazil, an educated, healthy, honest and happy Brazil," he wrote.
Fellow player Hulk also offered support but rejected the notion that the demonstrations represented a protest against the World Cup.