The former Manchester United man was suffering with a problem during the Champions League match with Valencia on December 10.
He was taken for an extensive medical examination and diagnosed with heart muscle inflammation.
The 29-year-old has missed Ajax’s last two games and will not rejoin training in January.
It is unclear when he will return, with Blind saying he is aiming to be back on the pitch ‘as soon as possible’.
An Ajax statement posted online said: “Daley Blind has been diagnosed with heart muscle inflammation.