The centre-back, who was treated for cancer last year, will be out of action for three months after an anomaly was detected during medical checks
Athletic Club defender Yeray requires chemotherapy after an anomaly was found during a medical examination on Monday.
Yeray, who made his senior debut last September, was diagnosed with testicular cancer in December and immediately had surgery to remove the tumour.
However, 22-year-old has had to leave the Spain Under-21 squad to undergo treatment and is expected to be sidelined for three months, Athletic confirmed.
"During a radiological check-up done on June 12, the latest of the follow-up tests done to monitor the progress of the testicular tumour that was detected and removed in December 2016, an anomaly (adenopathy) has been detected that needs to be treated and hence, in the coming days the player will undergo complementary treatment (chemotherapy) indicated by the specialists," a statement released on Tuesday read.