Dana White says the UFC is taking the "necessary steps" to address Conor McGregor and Khabib Nurmagomedov's "unacceptable" social media spat.
The fierce rivals have traded insulting jibes since McGregor announced his retirement from mixed martial arts last week.
McGregor backtracked on Wednesday by stating his intention to return to the Octagon.
UFC boss White then warned both fighters that their recent exchanges would not be tolerated.
"I am aware of the recent social media exchange between Khabib Nurmagomedov and Conor McGregor." White said in a statement.
"The ongoing situation has escalated to a level that is unacceptable. As such, we are taking the necessary steps to reach out to both athlete camps and this situation is being addressed by all parties internally."
Irishman McGregor had taken to Twitter earlier to reveal his plan to resume his career.
"I want to move forward, with my fans of all faiths and all backgrounds," the 30-year-old posted.
"All faiths challenge us to be our best selves. It is one world and one for all. Now see you in the Octagon."