Hunter Biden’s leading attorney has asked to withdraw from the case because he could be called in as a witness in future litigation involving the collapsed plea deal he brokered with prosecutors.

Lawyer Christopher Clark filed a motion with the Delaware judge who has presided over the case since the plea deal was announced.

“Based on recent developments, it appears that the negotiation and drafting of the plea agreement and diversion agreement will be contested, and Mr. Clark is a percipient witness to those issues,” Hunter Biden’s lawyers said in the filing, obtained by CBS News. “Under the ‘witness-advocate’ rule, it is inadvisable for Mr. Clark to continue as counsel in this case.”

Under the initial plea deal Clark brokered with U.S. Attorney David Weiss, Hunter was to plead guilty to misdemeanor tax charges and participate in a pre-trial diversion program to avoid felony gun possession charge. In exchange, Hunter was to receive broad immunity from future charges, including potential charges related to foreign influence peddling that congressional Republicans have alleged.

That deal fell apart in court earlier this month after U.S. District Court Judge Maryellen Noreika challenged the broad immunity provision as unprecedented.

Specifically, Hunter Biden would have pleaded guilty to not paying taxes on $1.5 million in income between 2017 and 2018 and entered into a separate deferred prosecution agreement for illegally possessing a gun while under the influence of drugs, which is a felony.

Clark filed a motion earlier this week arguing that prosecutors must honor the offer of a pre-trial diversion program on the gun charge as “valid and binding.”

On Friday, Attorney General Merrick Garland announced the appointment of U.S. Attorney David Weiss as special counsel to continue to oversee the “ongoing investigation” of Hunter Biden as well as “any other matters that arose or may arise from that investigation,” Garland said.

Many Republican lawmakers have criticized Weiss’s appointment, pointing out that he, like Clark, also helped assemble the accommodative plea deal in the first place. However, Weiss suggested in court papers Friday that he would consider taking Hunter Biden to trial on the tax charges. Critics have also pointed out that Weiss’s appointment is unusual given that special counsels are typically drawn from outside the government to ensure independence and impartiality.