Former Assembly Speaker Sheldon Silver earned himself a clean slate when his corruption conviction was overturned on appeal, winning a new trial and fresh presumption of innocence.

The same could not be said for the renowned cancer researcher who got $500,000 in shady grants that prosecutors said Silver funneled to him in an illegal quid pro quo. Dr. Robert Taub was fired by Columbia University shortly after FBI agents arrested Silver in 2015.

Now, on the eve of his Monday retrial, Silver desperately wants to keep the jury from wondering why Columbia canned Taub from his prestigious post as head of its since-shuttered Mesothelioma Center.

In an 11th-hour court filing, defense lawyers asked Manhattan federal Judge Valerie Caproni to warn jurors that Taub, again the prosecution’s star witness against Silver, will testify that he was fired by Columbia — but also order them “not to speculate as to why.”

An additional proposed instruction would have Caproni say: “Dr. Taub’s termination is not relevant to the charges against Mr. Silver and you are instructed not to consider it.”

Taub waged a protracted legal battle against Columbia following its 2015 decision to demote him with six months’ notice of dismissal from his $300,000-a-year gig.

That move came just one day after Silver’s arrest on allegations that include showering Taub with taxpayer funds in exchange for Taub steering cancer patients to the Weitz & Luxenberg law firm, which the feds say paid Silver, then working “of counsel” to the firm, more than $3 million for the referrals.

A state judge initially ruled that Taub couldn’t be fired without a hearing, but an appeals court reversed the decision.

Taub, 82, has grown sickly since he testified at Silver’s first trial in November 2015 and the retrial was delayed two weeks to accommodate his recovery from illnesses. He is to be among the first three witnesses, but he’ll be given a break every hour and have a health-care aide on hand.

The retrial is expected to largely reprise the one that saw Silver convicted on all counts and later sentenced to 12 years in prison — before an appeals court tossed the verdict while Silver remained free.

Silver’s successful appeal was based on a 2016 US Supreme Court ruling that reversed the conviction of former Virginia Gov. Bob McDonnell and limited the definition of “official act” in a corruption case.

Legal experts said the impact of the McDonnell decision would make it harder for the feds to convict Silver a second time, because revised jury instructions could exclude some of the most damning evidence from consideration.

Former federal prosecutor Harry Sandick said Silver’s retrial would provide a “laboratory test” for post-McDonnell corruption cases.

“The real scandal is not what is illegal but what is legal,” Sandick said.