Spain star Isco was forced off in his country's friendly against Costa Rica after being caught on a late challenge.
The Real Madrid midfielder was levelled by a dangerous tackle from Ticos centre-back Kendall Waston, who was shown a yellow card in the 62nd minute for the challenge.
The midfielder was, however, able to walk off the field, and Spain striker Alvaro Morata was optimistic after the game about his former Madrid team-mate's condition.
Isco's name could be added to Madrid's growing list of injuries, with Mateo Kovacic, Keylor Navas, Raphael Varane and Gareth Bale all currently sidelined.
The Blancos face city rivals Atletico at the Wanda Metropolitano in the Madrid derby next Saturday, and losing Isco would be another blow for Zinedine Zidane's side.