The Spain international picked up a knock in the opening stages of this week's encounter with Sevilla at the Santiago Bernabeu and was forced to leave the pitch after just nine minutes of play.
Ramos has since undergone a series of tests and Madrid have now confirmed the centre-back faces a spell on the sidelines due to a torn hamstring.
"Following tests carried out on Sergio Ramos by the Real Madrid medical service at the Sanitas La Moraleja Hospital, the player has been diagnosed with a torn hamstring in his left leg. His progress will be monitored," a statement on the club's official website reads.
The 28-year-old's injury means he will miss this weekend's derby with Atletico Madrid as well as the Champions League round-of-16 tie against Schalke, with head coach Carlo Ancelotti ready to turn to Raphael Varane and Nacho Fernandez during his absence.
"Ramos' injury is serious. He will be out for the next five weeks, but I believe in Nacho and Varane," the Madrid boss said at a press conference.
"They are good players and have plenty of enthusiasm."
Ramos has made 29 appearances in all competitions for Madrid so far this term, scoring six goals in the process.
