Swimming legend Ian Thorpe has admitted that he has struggled since his return to the pool earlier this year.
The five-time Olympic gold medallist retired in November 2006 but has come out of retirement with the hope of competing at London 2012.
"At the moment I'm not very close to being where I was before," the 28-year-old Australian said.
Thorpe, who has been working under new coach Gennadi Touretski in Switzerland, added that "it's a real struggle".
He continued: "I'm on track with the level that I thought I would be when we set out the time-frames when I came back but London is getting very close now.
"Training hasn't been easy. If it was then everyone would do it.
"On the whole I'm enjoying it but there are days when it's a struggle. It's really hard to do the training, especially if I'm down and I'm not swimming as well as I'd like.
"The most frustrating part is not being able to do something that you really want to do and remembering how you are supposed to do it."
With nine Olympic medals to his name, Thorpe is the most successful Australian Olympian of all-time. When he announced his retirement at the age of 24 he cited a lack of motivation.
The 'Thorpedo' said he was only going to take part in relays when he announced his comeback in Ferbuary. But he has since hinted that he could compete in individual races.
That would set up the prospect of a head-to-head battle in the 200 metres freestyle against American Michael Phelps, the man who has dominated the scene since Thorpe announced his retirement.
Phelps burst on to the scene by claiming eight gold medals at the 2008 Olympics in Beijing, breaking Mark Spitz's 36-year-old record for the most golds at a Games in the process.
Thorpe beat Phelps in what was billed as "the race of the century" in the 200m freestyle in Athens in 2004 and there is already a clamour for a rematch in the pool in London.
However, the Australian has insisted that he will not let such talk distract him from his comeback.
"It may happen. It's something that I know the media would love. They will put us as rivals where we are staring each other out in photos but Michael and I will have a laugh about it because we're friends," he added.
"I don't specifically think about beating him or anyone else.
"I train so that I can be in the best shape and perform at my best. As soon as you start worrying about other people then you lose a lot of energy."
Ian Thorpe will be part of the BBC Sport team commentating on the Great Salford Swim live on BBC Two and online from 1400-1530 BST on Sunday 15 May
He is also backing the Big Splash - an initiative to get more people swimming