Ronaldo has signed lucrative two-year contract with Al Nassr after leaving Manchester United back in November.
Saudi Arabia have often been widely criticised for their poor human rights record, which include executions and restriction of women rights.
Ronaldo is one of the biggest brands in sports with a huge following on social media.
At his unveiling on Tuesday, Ronaldo said he wanted to help the development of the game in Saudi Arabia, but Amnesty International, a global organisation that campaigns against human rights abuse, have charged the five-time Ballon D'or winner to make his presence felt off the field as well.
In a statement, Amnesty International's Middle East researcher Dana Ahmed said: "Al-Nassr's signing of Cristiano Ronaldo fits into a wider pattern of sportswashing in Saudi Arabia.
"It is highly likely that the Saudi authorities will promote Ronaldo's presence in the country as a means of distracting from the country's appalling human rights record.
"Instead of offering uncritical praise of Saudi Arabia, Ronaldo should use his considerable public platform to draw attention to human rights issues in the country.
"Saudi Arabia regularly executes people for crimes including murder, rape and drug smuggling.
"The authorities are also continuing their crackdown on freedom of expression and association, with heavy prison sentences handed down to human rights defenders, women's rights activists and other political activists.
"Cristiano Ronaldo shouldn't allow his fame and celebrity status to become a tool of Saudi sportswashing – he should use his time at Al-Nassr to speak out about the myriad human rights issues in the country."
