Real Madrid star Courtois did report to the camp ahead of the final two World Cup qualifiers, against Kazakhstan and Liechtenstein, but doctors confirmed an adductor issue that had been flagged by his club, in the wake of the draw against Rayo Vallecano in La Liga.
An official statement read: "Thibaut Courtois underwent the medical examination this afternoon by the RBFA medical staff. He will not be available for the upcoming international matches and will return to his club for further treatment."
The 33-year-old's absence opens the door for another keeper, and it is being predicted in the press that Nottingham Forest's Matz Sels will be handed the jersey for the long trip to Astana for Saturday's clash.