The Russians saw their hopes of reaching the second round suffer a blow on Sunday as they were beaten with two minutes to play by their fellow Europeans.
Kozlov and his teammates must now beat Algeria in their final group game if they want to book their place in the last 16.
"It's very difficult to draw any positives when you lose like that," Kozlov told FIFA.com.
"We're all disappointed about what happened late on, but we've still got a chance of continuing in the tournament. While that's the case, we can't start thinking about anything else."
Russia face Algeria in their Group H decider on Thursday.