Mikhail Gershkovich, who coached Russia from 1999 to 2002, said the real challenge awaited Russia if it beats the Slovaks in Bratislava to take a place in the play-offs.
"We must remember that a win over Slovaks would give us only a chance of making it to the play-offs, where an even more serious contender could be waiting," he said.
Gershkovich said the Russian team had many advantages in the game against Slovakia, which is currently in the second spot, one place ahead of Russia, in Group 3 on goal difference. Portugal has already qualified from the group in first place.
"First of all, the team is very skillful and fast," he said. "The Slovaks are very good at set plays and have a good defense."
The eventual second place team will play in a play-off match with a team from another group to book one of the finals place to Germany next year, which means the game on Wednesday is a decider for Group 3.