Danny went down injured during Zenit's 5-2 victory over Spartak Moscow on Saturday and was replaced by Javi Garcia after only 31 minutes into the game.
Zenit have confirmed that scans have revealed that Danny has suffered a rupture to his anterior cruciate ligament in his right knee which will require surgery.
It is estimated that Danny will be sidelined for eight to nine months and will therefore will not be able to represent Portugal in the Euros this summer in France.