The QMS
The manufacturer of a medical device is obliged to establish, document and implement a Quality Management System (QMS). Even thought the Medical Device Regulation MDR 2017/745 does not explicitly name the ISO 13485, it is the QMS international standard to work according to.
Further, the QMS has to be kept up-to-date and is subject to audit. Thus, the audit will most likely following ISO 13485, and having it not implemented will add additional risk to the audit.