Despite losing their opening two games in Europe, the Italian coach believes that his side have the quality to advance to the knockout stages
Speaking to reporters after the 3-2 home defeat to AC Milan, the former Udinese and Roma coach rued the mistakes of his side and praised the performance of opposing goalkeeper Christian Abbiati.
"Abbiati made some amazing saves – he literally plucked some balls away from the net," he said.
"Unfortunately the individual incidents did not go our way tonight but when you make too many mistakes, eventually you have to accept defeat.
"We didn't play to our full potential... If you want to become a big team you have to play well for 90 minutes, especially in this competition."
The Italian coach questioned the mentality of some of his players and feels that his side now have to secure all three points in their crunch tie against Anderlecht later this month.
"I have a feeling that the players forgot about the importance of this game, they did not take full responsibility," he said.
"However, we are not out yet, we can still qualify, but we have to start playing better and winning games immediately.
"I would be very angry if anybody in the team thinks it's over after these two defeats."
Zenit advanced through the group stages last year until they were knocked out by Benfica in the round of 16.