Canadian coach John Herdman expects "three groups of death" to emerge from Thursday's Olympic women's soccer draw in Rio de Janeiro.

The draw, for both the men's and women's fields, is being held at the historic Maracanã stadium.

"It's a scary draw, this one," said Herdman, who led the Canadian women to a memorable bronze medal four years ago in London.

Travel is one reason. But for Herdman a bigger factor is the improvement in the women's game, as shown by last summer's World Cup in Canada.

"People think teams like China, New Zealand, Costa Rica are like average teams," he said. "They're not. The Netherlands. They've all gone up (by) notches. And when I look at the draw now, even Colombia is a tough team. They beat the French 2-0 in their group stage (World Cup).

"So they're going to be three groups of death, bottom line," he added with a laugh. "And if you end up in Manaus, you've got some challenges ... And then if you end up in Rio, you've got challenges because if you have to stay in the Olympic Village, it changes everything in terms of everything you've done to prepare your team in tournament mode for the last 10 years of your career.

"Because the minute you have to work in the Village, all the rules change around how you operate."

That's because if the Canadians are in venues away from the Olympic Village, they'll stay in hotels. The experience will be the same as staying in "FIFA bubbles" during the World Cup. In the Village, the soccer players will be surrounded by other athletes in a more open, social environment.

The Olympic soccer venues are Belo Horizonte, Brasilia, Manaus, Rio de Janeiro, São Paulo and Salvador. Rio is home to two venues: the Maracanã and Olympic Stadium.

Manaus is located in the heart of the Amazon rainforest, some 4,275 kilometres northwest of Rio. Only two women's games are scheduled there.

How the Olympic draw works

Herdman will miss the draw because he is holding a camp for top prospects. Assistant coach Simon Eaddy will be in Rio.

The 12 teams on the women's side of the draw have been placed in four pots, based on the March 25 FIFA world rankings. Host Brazil, ranked eighth, is in Pot 1 with the top-ranked and defending Olympic champion Americans and No. 2 Germany. Pot 2 is made up of No. 4 France, No. 5 Australia, and No. 6 Sweden.

Canada, ranked 10th, is in Pot 3 with No. 12 China and No 16 New Zealand while Pot 4 consists of No. 24 Colombia, No. 54 South Africa and No. 95 Zimbabwe.

The goal is to keep teams from the same confederation away from each other in the pool phase. So Canada will escape the U.S., facing either Germany or Brazil. If drawn with Germany, the Canadians should avoid the powerful French.

As host country, Brazil will begin play in Rio with teams in its group playing two games there and one elsewhere (the pool features one game in Manaus). Teams in the other two pools will be based out of Belo Horizonte and São Paulo, playing two games in their host city before travelling for the third.

The top two teams from each of the three pools plus the two best third-place finishers will advance to the quarter-finals.

Restricted to 12 teams, the Olympic women's field is half the size of the World Cup.

The Olympic men's draw will also involve four pots: