Nessus scanner overview
Tenable provides an integration with IBM QRadar by using its Tenable.sc and Tenable.io platforms to address the needs of enterprise customers. For more information about Nessus APIs, see the A Clarfication about Nessus Professional blog by Tenable (https://www.tenable.com/blog/a-clarification-about-nessus-professional).
As of December 2018, Tenable officially removed support for Nessus APIs. As a result, Tenable does not support direct integration between Nessus and QRadar