The fallout from the failed IndyCar race continues to rain on Boston City Hall, with the former promoter slapping a $15 million malpractice suit on a top aide to Boston Mayor Martin J. Walsh and accusing him of causing the race to collapse.

The former CEO of the Boston Grand Prix, John Casey, alleges in a complaint filed this week that Austin Blackmon, Walsh’s chief of Environment and Energy, was “singularly responsible” for the race’s demise because he failed to flag a needed flood zone permit before it was too late.

“His (Blackmon’s) negligence was responsible for millions of taxpayer monies to be wasted in addition to millions of Boston Grand Prix monies to be wasted,” Casey’s complaint states.

Casey’s lawsuit, filed this week in Suffolk Superior Court, is the latest legal shot fired in the long-running IndyCar race fiasco, which has been a major embarrassment for Walsh, the race’s chief cheerleader.

A spokeswoman for Walsh said the city would have no comment on Casey’s lawsuit.

The legal action is unusual because it targets Blackmon personally and not the city. One legal expert familiar with the case said he expects defense lawyers would try to seek a quick dismissal of the complaint.

Casey himself has been targeted in numerous civil lawsuits due to the race’s cancellation, including one from Attorney General Maura Healey. That case was settled earlier this month when Casey agreed to pay a $50,000 penalty and be permanently barred from promoting events in exchange for Healey dropping the lawsuit.

Casey is also in the middle of bankruptcy proceedings, in which the trustee claims the former promoter spent hundreds of thousands of dollars of Grand Prix money for his own use.

The IndyCar race, called the Boston Grand Prix and scheduled to take place last fall, was canceled in April 2016 after promoters failed to secure approval for a permit to build part of the course through a newly designated flood zone in the Seaport District.

Casey claims he wasn’t told by Blackmon about the needed permit until mid-March.

“By the time Blackmon revealed this issue, it was too late to obtain the necessary permits to allow the race to happen,” Casey states in his new complaint.

The complaint also states that “Blackmon’s negligence rises above” any protection he gets as a municipal employee acting on behalf of the city of Boston.

Casey claims in the suit that because of the race’s demise he has “suffered … a loss of reputation, diminished health, loss of business, and several million in damages.”