The promising youngster could sit out Los Blancos' league match at the weekend after picking up a minor problem when on duty with his country's Under-21 team
The young defender sustained a muscular problem while away on international duty with France Under-21s, and missed Wednesday's regular training session due to the knock.
Varane was restricted to doing individual exercises with the Madrid physio, and it remains to be seen whether he will be fully match fit in time for Saturday's clash.
The Frenchman's injury is yet another blow for Mourinho after Fabio Coentrao, Marcelo and Alvaro Arbeloa all picked up physical problems as well with their respective national sides.
Saturday's match at the Santiago Bernabeu is scheduled to kick off at 18:00CET.