The January 17 interview with Oprah Winfrey will be Armstrong's first since receiving a lifetime ban and being stripped of his seven Tour de France titles in October for doping charges the American has until now vehemently denied.
"I don't think he goes there to say that he's innocent and that he didn't do anything," Schleck told reporters on his arrival in Adelaide ahead of this month's Tour Down Under.
"I believe he does it for a good reason," said the 27-year-old, who was retroactively awarded the 2010 Tour de France last year after original winner Alberto Contador was stripped of the victory for a doping offence.
"But if he confesses? We don't know."
The RadioShack rider said the Armstrong revelations came as a surprise but he believes the sport has moved on since the drugs-tainted period when the American dominated cycling's most prestigious race from 1999 to 2005.
"It shocked me. Somehow, even three or four years ago, we maybe knew that the Lance Armstrong era was not the cleanest in cycling so far," Schleck added.
"But I believe that since 2005 and 2006 with the biological passport, everything changed for the young generation."
Cycling would still come across the odd dope cheat, said Schleck, whose brother Frank will discover the outcome of a disciplinary hearing on January 30 after testing positive for a banned diuretic during last year's Tour de France.
"There will still be some guys positive again this year," he said. "But that's not necessarily a bad sign. That's a sign that the system works. I don't believe in cycling they dope more.
"In every sport, there's cheaters but in cycling they get caught. That's a good thing."
The six stage Tour Down Under takes place from Jan. 22-27 in South Australia.