Law professor Tey Tsun Hang may be representing himself in court as the sex-for-grades trial gets underway on Thursday morning.

The dramatic twist came barely an hour into first day of the nine-day hearing, after Tey's lawyer Peter Low told the court on his client's behalf, that Tey would like to "play an active role" in court proceedings.

When asked to elaborate, Mr Low explained that Tey would like to cross-examine some of the prosecution witnesses, to which the prosecution objected since he is already represented by defence counsel.

Tey then told the court that he would discharge Mr Low as his lawyer and told the court that he will fight the case on his own.

The former associate professor at the National University of Singapore faces six charges of corruptly obtaining sex and gifts from a former student in exchange for better grades.

The alleged offences took place between May and July 2010.

The 41-year-old has since been suspended from duty by the university, which has also launched an internal investigation.

The trial is expected to last until Jan 22, and the prosecution has lined up 12 witnesses, including the female student in the centre of the case, Ms Darinne Ko Wen Hui, 23.

Besides Ms Ko, they are likely to include the various retailers who sold her the gifts she gave to Tey, and officers from the Corrupt Practices Investigation Bureau (CPIB) who questioned him.