Five-time Olympic gold medallist Ian Thorpe will compete in his first international meeting for five years at the World Cup in Singapore on Friday.
The Australian, 29, retired in 2006 but announced earlier this year he was returning, with London 2012 the target.
"I am on track and I'm swimming well," Thorpe told BBC Sport.
"I have to manage my expectations though. I go from thinking I am one of the best swimmers in the world - but I haven't competed in nearly five years."
Thorpe will compete in the 100m butterfly and 100m individual medley in Singapore. His presence has led to huge interest in a normally low-key event.
Similar attention is likely to follow Thorpe as he competes in the World Cup meetings in Beijing and Tokyo later this month.
"I'm excited and I'm anxious about it," Thorpe added.
"There's pressure as people would like to see me swim well. I'm sure after the first competition I'll be relaxed about that but the first race may be a bit odd.
"I'm where I thought I would be [at this stage of the comeback], plus or minus 5 to 10% - but I won't tell people which way that is at the moment."
In an exclusive interview with the BBC, the three-time Sydney Olympic Games gold medallist admitted he felt he was more likely to fail than succeed in his bid to reach the London 2012 Olympics.
"It's difficult, you take a bit of an ego-bashing because you're so good at doing the distance [400m freestyle] training," he said.
"To come back and feel like you're behind is hard but I had to do it. It has meant I'm a better swimmer now, technically, than I was."
After competing in the World Cup this month, Thorpe will have just over three months to reach peak condition for Australia's Olympic trials in March 2012.
Thorpe is not the only Australian making a comeback in Singapore, as triple Olympic champion Libby Trickett returns to action for the first time since 2009.
The 26-year-old will compete in the 50m and 100m freestyle events.