Messi and Ronaldo have been named the top two players in the world in voting for the Ballon d'Or for the past five years, with the Argentine winning the award three times in that period.
Ronaldo is in line for another Pichichi award this season, as the Portuguese currently leads the Spanish goalscoring charts with 28 goals - although Messi boasts a better minutes-per-goal rate.
When asked about the differences between the two players, Xavi, now playing in Qatar, told The New Arab: "Ronaldo is a goalscorer, and Messi is also a goalscorer; however, Messi is a much better team player than Ronaldo.
"I think Messi is the best footballer in the world. In football, there are two important elements: fitness and intelligence. Ronaldo is very fit but Messi has both the fitness as well as the intelligence, so simply put he is better."
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Xavi also believes that Paris Saint-Germain and Bayern Munich, not Real Madrid, are Barcelona's main rivals in this season's Champions League.
"Obviously, I want my team Barcelona to win the title," he said. "I think they are the most likely to win along with Paris Saint-Germain and Bayern Munich.
"But of course we must be wary of Real Madrid, because when they have unstable results in the league they usually play better in the Champions League.
"But I still think Barcelona is the likeliest team to win."