Psychiatrist Tommy Tan, who was supposed to testify for the defence in the sex-for-grades corruption trial involving former law professor Tey Tsun Hang, will need to appear in court tomorrow or risk being arrested.

This after the consultant psychiatrist at the Novena Psychiatric Clinic had repeatedly failed to show up in court despite having been subpoenaed.

Chief District Judge Tan Siong Thye on Tuesday ordered a warrant of arrest to be issued on Dr Tan if he failed to turn up in court again.

The judge, in giving Dr Tan "one last chance", told the defence to convey to the psychiatrist consequences of the failure to attend Court at 2.30pm on Wednesday.

"In the meantime I'm going to issue a warrant of arrest against him," said Chief District Judge Tan. "Either he comes voluntarily to this Court, or a warrant of arrest is served on him.... If he comes voluntarily then the warrant will not be necessary."

Dr Tan had first failed to show up in April due to an eye operation and was then told to come on Tuesday morning, but claimed he was busy. The judge then adjourned the case for the defence to make necessary arrangements for Dr Tan to come in the afternoon, but he still failed to show up.

Instead, he had written a letter to defence counsel Peter Low, saying that he had "six patients scheduled to see me this afternoon ... they have been waiting ... since I was on medical leave for more than six weeks".

Tey, 42, had sought Dr Tan's urgent psychiatric treatment on April 9, 2012, claiming to be traumatised by his time at the Corrupt Practices Investigation Bureau on April 5, 2012, when he had made two statements.

Tey faces six charges of corruptly obtaining gifts and sex from former student Ms Darinne Ko between May and July 2010.