Thorpe has been unable to come close to his world-beating best following his return from a four-year retirement last February.
The 29-year-old will attempt to qualify for a third Olympics at the Australian Swimming Championships in Adelaide next week, but is preparing to miss out.
"The most realistic outcome of this is that I will most likely fail," he told Australian TV station Network Ten.
"All of the expectation, that desire to see me do well, it exists for me in a way that it doesn't exist for other people."
Thorpe claimed 11 world titles and 13 world records in his pomp but has found himself pinning his hopes on a top-six berth in the 100 or 200metres freestyle to earn himself a place on the relay team.
"I wish I had another six months to do this," he said.
"I wish I had more time to do it. I have to be swimming well. I have to be swimming fast as well in both of my races."
Despite that Thorpe said he would not retire should he fail to make London.
"It will probably be the last time I will be able to do this so I want to be able to make the most of it," Thorpe said.
"So I'll probably swim for at least a year or two after the Games."