Though Messi has gone on to become one of the undisputed best and most successful players ever, he started at Barcelona under the wing of Ronaldinho, who was playing at his effervescent best around the time the Argentine made his debut for the club.
Messi has won the Ballon d'Or on six occasions - five more than Ronaldinho, while he has won significantly more leagues, more Champions Leagues, and scored more goals.
However, for Deulofeu, who did spent a short period playing with Messi, the Brazilian is above everyone in talent on the pitch.
"For me, Ronaldinho is the best player in history," Deulofeu told the official Serie A website.
"I met him, I went to see a match at the Camp Nou and he was sitting next to me. It was a wonderful experience.
"Messi is incredible too, I like him very much. I played with him for six months and he is a nice person, a great player.
"The whole world knows about Messi."
Following Watford's relegation last season, Deulofeu joined Udinese on a season-long loan deal for his second stint in Italy after featuring for Milan in 2017. Although he still harbours a soft spot for the Rossoneri, his focus is now on impressing the Udinese faithful.
"I had a wonderful experience in Serie A the last time, as I played a lot and I played well," he said.