Messi and Ronaldo are widely regarded by many as the two greatest to have ever played the sport, with their goals and brilliance defining an entire era of the sport.
The pair boasts 11 Ballon d'Ors between them, with Messi collecting his sixth back in December to move one ahead of Ronaldo.
However, despite their relative parity in terms of goals and accolade, Beckham is a firm believer that Messi is the superior player of the two.
"Messi is unique as a player and there isn't anybody else like him," Beckham told Argentinean broadcaster Télam.
"Both he and Cristiano, who is not at the same level as Messi, are head and shoulders above the rest."
Recalling his encounter with the Argentina captain, Beckham added: "We were ahead and he came on and Barcelona scored.
"Despite my age, I enjoyed playing and the team played well in both legs. We did things that we can be proud of. They didn't beat us."