As teams rushed to submit their final squad lists, Iran named Sardar Azmoun, their star player who has expressed support for the demonstrations in his homeland, in their final squad.
Azmoun, who plays for German club Bayer Leverkusen, has posted several social media messages in support of the protests that were sparked by the death of 22-year-old Mahsa Amini.
Dozens of people, mainly demonstrators but also security personnel, have been killed during the protests, which the authorities have branded as "riots".
Activists have called on fans attending Iran's matches in Qatar to chant Amini's name.
Sunday's kickoff marks the culmination of Qatar's extraordinary campaign first to win the vote to land the tournament and then embark on a spending spree of tens of billions of dollars to build stadiums and infrastructure.
World governing body FIFA's pleas to "focus on the football" have struggled to be heard as the countdown to kick-off has only increased scrutiny of the country's treatment of migrant workers, women and the LGBTQ community.
Labourers from South Asia have been at the centre of an often acrimonious dispute over deaths, injuries and working conditions since Qatar was awarded the World Cup in 2010.
Amnesty International has urged FIFA to commit to compensating migrant workers "for abuses suffered" during preparations for the tournament.
Qatar has angrily rebuffed most of the attacks and local media have blasted the "arrogance" of some Western countries.
Australian players refused to enlarge on their comments about Qatar's rights record on Monday, saying they were fully focused on a daunting opening match against defending champions France.
The Socceroos released a video last month featuring 16 players, in which they spoke out against rights abuses in the Gulf state, although they acknowledged progress had been made.
"To be honest I think we timed things well with what was said," Australia forward Mitchell Duke, who featured in the video, said at the team's training base in Doha.
"We've done that purposely before we all came to the camp because our main priority now, once we turned up, was just to focus on the football side of things."
Qatar, a country of barely three million people and one of the world's biggest producers of natural gas, has spent lavishly.
New stadiums have cost more than $6.5 billion and a driverless metro system with a price tag of $36 billion serves five of the eight venues.
Some estimates put total infrastructure spending over the past decade at $200 billion.
Organisers have predicted more than one million fans will travel to Qatar.
Tournament chiefs say that 2.9 million of the 3.1 million tickets have been sold, with fans waiting outside ticketing centres in hopes of seeing top games.
Qatar announced its first arrests of World Cup ticket touts on Monday, with three foreign men detained outside official ticketing centres in Doha. No details were given of their nationality.