Diego Costa has been diagnosed with a cervical disc herniation in a fresh blow to goal-shy Atletico Madrid.
Scans undertaken in recent days identified the issue, which relates to the spine, but a rehabilitation programme has not yet been formulated.
Atletico said the 31-year-old requires special neurosurgery assessment before the full scale of the injury can be established.
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"The medical services of the club have conducted radiological tests of Diego Costa to assess the cervical discomfort suffered in recent days," read an Atletico statement.
"These tests have determined that the forward suffers a cervical disc herniation.