"Moussa Sissoko got a head injury in the game against Middlesbrough and he is out," Pochettino told the club's website (www.tottenhamhotspur.com) on Monday.
"We can't rule out concussion and so we are treating it this way."
Eric Dier, Danny Rose, Mousa Dembele and Harry Kane also miss the trip to Russia as Spurs look to bounce back from their Group E opening game defeat against Monaco at Wembley Stadium.
Rose suffered a hamstring injury on England duty this month, while Dier and Dembele left the field early during the 1-0 win against Sunderland.
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Kane, last season's Premier League top scorer, went off with an ankle injury against Sunderland.
(Reporting by Nivedita Shankar in Bengaluru, editing by Ed Osmond)
