AC Milan have revealed that Antonio Cassano will require 'a small heart operation' after suffering an ischaemic stroke.
The striker fell ill in the early hours of Sunday morning and was rushed to hospital after developing problems with his vision, speech and movement.
It was initially unclear what the problem was, with the Italy international having stepped off the bench in Milan's 3-2 victory over Roma on Saturday.
It has, however, now been confirmed that the 29-year-old is struggling with a heart defect and will be sidelined for 'several months'.
"Having consulted with the Policlinico (hospital) in Milan, AC Milan can confirm that Antonio Cassano suffered from a cerebral problem related to an ischaemic stroke," Milan said in a statement.
"The instrumental and neurological examinations needed 72 hours to be developed and demonstrated a small problem in the cerebral area which has not caused lasting damage.
"The cause has been identified as a hole between the (left and right) atriums (in the heart) which could only be detected by sophisticated equipment.
"Therapy should result in a rapid recovery and improvement in his clinical condition, which is good.
"The footballer will undergo in the coming days a small heart operation (to close the hole) and the recovery period before returning to sporting activity will be several months."