Hindenburg Research faulted the insurer for not disclosing it was under investigation by the U.S. Department of Justice.
The proposed transaction is being reviewed over antitrust concerns.
Goldman Sachs also agreed to pay more than $2.9 billion as part of a deferred prosecution agreement with the U.S. Department of Justice.
The investigation involves whether the company shifted sales from quarter to quarter to make results appear stronger.
The company made a deal to resolve federal investigations into the sales and marketing of an opioid addiction treatment by its former business Indivior.
