Actually there is a way.. After some investigation.
Quote:
5.7.3. An Athlete who gives notice of retirement to UFC, or has otherwise ceased
to have a contractual relationship with UFC due to Athlete-Initiated
Inactivity, may not resume competing in UFC Bouts until he/she has given
UFC written notice of his/her intent to resume competing and has made
him/herself available for Testing for a period of six months before returning
to competition.
UFC may grant an exemption to the six-month written
notice rule in exceptional circumstances or where the strict application of
that rule would be manifestly unfair to an Athlete provided that in either
instance the Athlete provides a minimum of two negative Samples before
returning
Source:
https://ufc.usada.org/wp-content/upload ... icy-EN.pdfSo I suppose it means that if they find it proper they can make an exception and allow McGregor to fight after two negative tests.