Isco Alarcón will miss Real Madrid's derby against Atletico Madrid at the Wanda Metropolitano on Saturday after dropping out of training on Friday.
The Spain midfielder did start the session at Valdebebas but was unable to finish it after feeling a problem in his back.
Isco joins Marcos Llorente on the sidelines, who was injured in Wednesday's Copa del Rey draw with Barcelona and will be out for a month.
It's the third time Isco will have been left out of a matchday squad by Santiago Solari, who dropped him for the Champions League game against Roma and left him out for the Copa trip to Melilla.
He has spent the majority of Solari's spell on the bench -- as was the case against Barcelona in midweek -- and has found chances hard to come by under the Argentine.
On Thursday, Isco courted controversy with a social media post in which he complained he has not been given the same opportunities as some of his teammates.