Spain are yet to find their best form but are still dangerous, says their former midfielder Albert Riera.
"Spain are yet to show their best form at the tournament, but they are still Spain, they control the ball perfectly, up to 70% of the match, and that reduces Russia's chances of success," he said.
However, he added that Spain had already conceded five goals in their three matches during the group stage, meaning that Russia should be able to create goalscoring opportunities.
"It shows that Russia's national team will also create chances - but only one team will advance. If someone is to knock out our team from the tournament, I'd rather this team was Russia," he added.
The game will take place at Moscow's Luzhniki stadium on Monday morning AEST.