“Isco has been diagnosed with a muscular injury in the right femoral biceps,” said Real in a statement.
The club have not given a time frame for the midfielder’s return but said “his recovery will continue to be monitored”.
According to sports daily AS, recovery time for this kind of injury is between two to three weeks.
That would rule him out of the Liga games against Villarreal and possibly Levante on September 14.
It is another setback for Zinedine Zidane’s team which already has a lengthy injury list featuring Eden Hazard, James Rodriguez, Brahim Díaz, Rodrygo and Marco Asensio.