Olympic chiefs have demanded answers from Belarus before the close of play on Tuesday over the saga involving sprinter Krystsina Tsimanouskaya.
Tsimanouskaya refused to board a flight home from Japan after allegedly being taken to the airport against her will, having publicly criticised her team's organisation on social media.
She competed in just one event, finishing fourth in a 100 metres heat, before being pulled out of the Games by Belarusian officials. Due to also compete in the 200m, she claimed a Belarusian coach entered her for the 4x400m relay despite her never racing in the event before.
Tsimanouskaya suggested that was a result of members of the team being considered ineligible due to not completing enough doping tests.
The Belarusian Sport Solidarity Foundation indicated Tsimanouskaya feared for her life upon returning to Minsk. The country is under the authoritarian leadership of president Alexander Lukashenko, whose son Viktor heads the national Olympic committee (NOC). Both men were banned last December from attending Tokyo 2020.
Now the International Olympic Committee (IOC) is stepping up its probe into what occurred.
IOC spokesperson Mark Adams said on Tuesday: "We've asked for a report from the [Belarusian] NOC today. We requested it yesterday, we want it today.
"We have decided to launch, not surprisingly, a formal investigation, which will be led by the IOC administration. We need to establish the full facts, we need to hear everyone involved. That obviously can take time."
Tsimanouskaya has been granted a Polish visa for now, and Adams said the 24-year-old spoke to the IOC twice on Monday, assuring that she now feels "safe and secure".
She has had police protection since alerting officers at Haneda airport to her situation.
"We've also now contacted the NOC of Poland," Adams said. "In terms of what the IOC can do for her in terms of her future we have talked to them with regard to her sport after her arrival in Warsaw, if that is where she does indeed choose to end up."