All nations except Saudi Arabia have confirmed that women athletes will participate in the London 2012 Olympics, Human Rights Watch said on Wednesday.
As the clock ticks down to the July opening ceremony, the US-based group said time was running out for the international community to insist that the Saudi government allow women to participate.
The International Olympic Committee's executive board is currently meeting in Quebec City to hear reports on the upcoming Games.
"Saudi Arabia is the last holdout denying women and girls the ability to take part in sports," said Sarah Leah Whitson, Middle East director at Human Rights Watch.
"The Saudi government's position should trigger serious scrutiny by the Olympic family," Whitson said.
"The dismal and unequal conditions for women and girls who seek to practice sports in Saudi Arabia need to change now."
At the 2008 Beijing Olympics, only Qatar, Brunei, and Saudi Arabia fielded all-male teams. This year, Qatar and Brunei have confirmed they will send female athletes as part of their teams for the first time.
In April, Prince Nawwaf al-Faisal, the Saudi sports minister and head of the Saudi National Olympic Committee, said the Gulf kingdom was not "embracing any female Saudi participation in the Olympics".
In February, Human Rights Watch released a report which set out how it sees the Saudi government systematically discriminates against women seeking to practice sports.
"The Saudi National Olympic Committee should be helping, not blocking, aspiring women athletes," Whitson said.
"This is a moment when the world should also tee up pressure to roll back discriminatory practices more broadly."
Saudi government officials have written to Human Rights Watch that the country is evaluating girls' physical education in schools.
"The IOC's leaders deserve credit for their work to bring more women to the Olympic playing field," Whitson said. "But a durable and meaningful victory will come only when the Saudi government stops denying millions of girls the chance to take part in sports."