Prostitution is legal in Singapore, but the prostitute must be at least 18 years old.
A lawyer for Buergrin, who was the head of operations for the Swiss bank in Singapore, claims that he was tricked by the girl and her pimp.
"The prostitute, in a conspiracy with the pimp, had deceived the accused as to her true age and thereby intentionally induced him to engage her services," his lawyer Selva Naidu said in a written statement released to journalists.
The prosecution said the website advertised the girl as an "18-year-old polytechnic student".
Fifty other men, both foreign and local, have also been charged with allegedly having sex with the underage Singaporean prostitute, the report said. She is now 20 years old, according to Bloomberg News.
Buergrin is married with two kids, according to Bloomberg.
The maximum jail time for paid sex with someone under 18 in Singapore is seven years.