Australia will be without Olympian Courtney Atkinson for this Sunday's world championship triathlon series opener, but the news is promising on Emma Moffatt.

Atkinson has pulled out of the race, which starts and finishes at the Sydney Opera House, as he continues to recover from a virus.

Moffatt has been in doubt as she recovers from the shoulder fracture suffered in a January bike crash, but some strong swim sessions have Triathlon Australia (TA) confident about her status.

Atkinson was 11th late last month at the World Cup round in Mooloolaba, but pulled out of Sydney after recovering poorly from the race.

"My recovery from Mooloolaba wasn't as good as expected and I had some unexpected complications ongoing from the illness I was carrying," Atkinson said in a TA statement.

"It is a long season with 10 to 15 races planned over the next five months, so this is a small hiccup in a big year.

"I am so close to being 100 per cent that it is such a hard decision not to race our home world championship event, but I think it is the right decision considering my aim is to win the world championship (series) and 90 per cent of that racing will be in Europe in two to four months' time.

"One race can't win the whole series, but interrupted preparation can cause ongoing problems for the whole year."

Atkinson's absence means the top Australian chance in the men's race will be Brad Kahlefeldt, who won Mooloolaba. They were team-mates at the Beijing Olympics.

TA will know in the next day or so whether Moffatt is a definite starter in Sydney as she starts her world title defence.

"We're yet to make a decision on Emma - that could take up to 48 hours - but at this stage she looks OK," said TA high performance manager Michael Flynn.

"The final decision rests with Emma and we'll give her every possible chance."

The women's team is already without Olympic champion Emma Snowsill, who is not yet at race fitness after recovering from injury and illness in the last few months.

AAP