Messi scored a hat-trick when Ajax travelled to Catalonia in the group stages last season, but former Barca defender De Boer believes that the Argentine is an even better player than he was last term.
"Messi's quality is such that he can score from any position. I believe he is playing more aggressively now than last season. He always want to play, he never wants to be substituted," he told uefa.com.
"It is no accident that he was named the best player in the world on several occasions. It is unbelievable to have set all those records at such a young age. For me, he is the best player in the world. Not just because of his goals − he also has made many assists over the last couple of years. A complete player."
Messi has scored eight times in 10 games this season.