World Cup hosts Russia look set to be without Aleksandr Kokorin after the Zenit striker ruptured cruciate ligaments in his right knee on Thursday.
Kokorin left the field after eight minutes of Zenit's Europa League clash with RB Leipzig, the last-16 second leg ending 1-1 to send the German side through 3-2 on aggregate.
The 26-year-old was seen clutching his right knee as he was substituted and Zenit confirmed on Friday that the diagnosis did not look good.
"Aleksandr Kokorin has been diagnosed with a rupture of the cruciate ligaments in his right knee," a club statement read.