Sheldon Silver leaves federal court on May 3, 2016. Photo: Rick Kopstein.

Citing health issues for a key witness in the second bribery trial of former New York State Assembly Speaker Sheldon Silver, the judge presiding over the case has postponed the start of the trial by one week, to April 30.

U.S. District Judge Valerie Caproni of the Southern District of New York ruled that voir dire in Silver’s trial is still set to begin on April 16; at a pretrial conference on Tuesday, the judge said the trial is expected to last between four and six weeks.

Prosecutors said during the conference that witness Robert Taub, a Columbia University oncologist who took part in a scheme that resulted in Silver pocketing $3 million in legal referral fees, may have to undergo surgery.

Silver, a Manhattan Democrat who was once a powerhouse of New York politics and one of the so-called “three men in a room” who charted the course for major policy decisions in the state, was convicted in November 2015 of honest services fraud, extortion and money laundering for running two alleged kickback schemes.

In the first scheme, Silver allegedly secured state grants for Taub, who in turn referred asbestos patients to personal injury boutique Weitz & Luxenberg, where Silver was of counsel.

Legal referral fees were also at the heart of the second scheme, in which Silver allegedly referred developer Glenwood Management to real estate law firm Goldberg & Iryami to appeal its tax rates, and is accused of returning the favor by pushing favorable tax and rent regulation legislation in Albany.

But last year, the U.S. Court of Appeals for the Second Circuit threw out Silver’s conviction, citing a U.S. Supreme Court ruling in another public corruption case that narrowed the definition of what counts as an “official act” under federal bribery statutes.