The French centre-back played the full 90 minutes of last week’s 1-1 draw with Chelsea in Madrid that saw Karim Benzema cancel out Christian Pulisic’s opener in the driving rain, though was forced off at half-time of Saturday’s 2-0 LaLiga triumph over Osasuna, subsequently undergoing a scan.
Los Blancos have now confirmed that Varane has been diagnosed with an injury to the right abductor muscle, with his recovery set to be monitored.
It is another cruel blow for the 28-year-old, who missed the Champions League quarter-final matches against Liverpool after testing positive for Covid-19.
Madrid captain Sergio Ramos - who trained on Monday - is expected to return to action against Chelsea after a calf injury kept him sidelined for nine matches, with Eder Militao likely to partner the experienced skipper with Varane sidelined.
Nacho - who replaced Varane for the second half against Osasuna - would provide cover from the bench.
Left-back Ferland Mendy could also return at Stamford Bridge, while midfielder Fede Valverde will need to return another negative coronavirus test in order to travel to west London.
Real Madrid right-back Dani Carvajal and winger Lucas Vazquez are still out, though Marcelo is expected to fly out to join his team-mates later than usual after being randomly selected to monitor a polling station during local elections on Tuesday.