Leicester have suffered so far in the Premier League but despite their troubles, optimism is high regarding their Champions League hopes.
Sissoko, 27, was substituted during Saturday's 2-1 Premier League win at Middlesbrough with concussion and has not recovered in time to face CSKA.
Around 250 Spurs fans are expected in Russia, and both the UK Foreign Office and the club have advised them not to show their colours in the city.
"We badly wanted to reach the final, but Atletico was more efficient in front of goal. We have plenty to rectify," Vidal said.
Pep Guardiola's Manchester City travel to Celtic in the Champions League with both the manager and club on the cusp of some big milestones.