A trial of City Comptroller John Liu's former campaign treasurer and a fundraiser that has seemed to temper enthusiasm for his expected mayoral run got delayed indefinitely Tuesday after one of the defendants was involuntarily hospitalized for treatment of a mental health condition.

U.S. District Judge Richard Sullivan announced the development at a hearing a day after the trial was originally scheduled to start. Sullivan did not elaborate on the illness of the former fundraiser, Xing "Oliver" Wu Pan, except to say he was undergoing treatment and it was unclear when he would be recovered enough for trial. He sealed some records related to the illness.

But he said he would direct authorities to seek a diagnosis and opinion on Pan's mental competency for trial by Friday. If the hospital cannot provide it, the judge said he would seek to appoint an expert to determine Pan's status.

The judge set an April 15 date for the trial but said he reserved the right to begin it sooner if Pan is ready. He asked Gerald Lefcourt, the attorney for Liu's campaign treasurer and co-defendant — Jia "Jenny" Hou — if he wanted to renew a request he had made last year for a separate trial. He said he did not because he hopes to question Pan on the witness stand on his client's behalf.

Both defendants have pleaded not guilty. They were charged with conspiring to use straw donors to evade campaign finance laws.

The 46-year-old Liu — the city's fiscal watchdog — is not charged and is unlikely to testify, but the trial was widely viewed as a hurdle to his unannounced but highly anticipated Democratic campaign for mayor. It is expected to last several weeks and comes just as campaigning begins in earnest for the competition to replace term-limited Mayor Michael Bloomberg, who is finishing a third term.

The judge called the trial's delay unusual but among the kinds of things that arise in criminal cases.