"(Varane) has been diagnosed with a muscle injury to the adductor longus in his right leg," said Madrid in a statement Tuesday.
Spanish media reports suggested the French defender will be sidelined until late November, leaving interim coach Santiago Solari short of options in central defence.
La Liga clubs can return to full training from Monday
Solari was appointed on Monday after Julen Lopetegui was sacked following a dismal start to the season, with Madrid languishing ninth in La Liga.
Striker Mariano Diaz is also set to miss 10 days with a hamstring injury.
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