Isco has become the eighth Real Madrid player to pick up an injury this summer after the club announced on Wednesday that the midfielder has a thigh problem.
James Rodriguez was ruled out for two to three weeks on Monday with a calf injury and now Isco will be sidelined for a similar amount of time.
"After the tests carried out today on our player Isco by the Real Madrid Medical Services, he has been diagnosed with a muscle injury in the right biceps femoral," the club said on their website on Wednesday.
"His recovery will continue to be assessed," they added.
Isco played 68 minutes of Madrid's 1-1 draw with Valladolid at the Santiago Bernabeu on Saturday and was replaced by Luka Jovic.
The Spain international ill now miss Real's trip to Villarreal in La Liga on Sunday, but could be back for Los Blancos after the forthcoming international break.
Marco Asensio is sidelined with a long-term injury picked up in pre-season, while Eden Hazard, Brahim Diaz, James and Rodrygo are all currently laid low.
Thibaut Courtois and Jovic also had spells out ahead of the season start.
