"Following tests carried out today (Wednesday) by Real Madrid's medical team, our player Eder Militao has been diagnosed with a muscle injury" to his groin, the club said in a statement.
The Brazilian felt a sharp pain in the 58th minute of Tuesday's international friendly against Tunisia in Lille, which ended 1-1, prompting him to ask to come off.
Spanish media have reported the centre-back will be out for around two weeks, meaning he would miss Sunday's La Liga clash with Elche and next week's trip to Girona, as well as next Wednesday's Champions League tie away to Olympiacos.