Danny will miss out on the chance to represent Portugal at Euro 2016 as he requires surgery on a knee problem.
Attacking midfielder Danny sustained the injury in the first half of Zenit's 5-2 victory over Spartak Moscow on Saturday and was replaced by Javi Garcia after just 31 minutes.
The club have confirmed that subsequent examinations have revealed a rupture to the anterior cruciate ligament in the right knee that will need to be operated on.
Zenit estimate Danny will be sidelined for eight to nine months as a result, with the captain to miss their Premier League run-in and Portugal's European Championship campaign in France this year.
It is a bitter blow for the Portuguese, who missed out on a place at Euro 2012 with a similar injury to the right knee.
On Thursday, left-back Fabio Coentrao was ruled out of the tournament in France due to a thigh injury that requires surgery.
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