“I know from my conversations with [Russian President Vladimir] Putin that he [does not accept] phrases like when Barack Obama said Russia was a regional power. What does that mean? You can't talk about Russia like that,” Juncker told a conference in the southern German town of Passau.
“We must, I say frankly, treat Russia properly,” he said, “Russia should be treated as an equal.”
Russia began a bombing campaign in Syria last week, radically changing the course of the four-and-a-half-year conflict and providing a massive boost to the regime of President Bashar al-Assad.
Moscow's relations with the West were already at a post-Cold War low after last year's annexation of Ukraine's Crimea region and its subsequent support of rebels in eastern Ukraine.
Juncker, while urging a new stance to Moscow, stressed that Russia must also “make huge advances”, adding that its role in Crimea and east Ukraine was unacceptable.
Europe and the US have imposed sanctions on Russia as a result of its annexation of Crimea early last year.
Western nations have also been highly critical of Russia's military intervention in Syria, accusing Moscow of seeking to prop up the regime of Assad more than tackling the Islamic State jihadists operating there.