Messi is constantly compared to fellow Argentine Diego Maradona and has arguably surpassed his compatriot in terms of achievements at club level, but many point to the World Cup when judging the Barcelona forward alongside the former Napoli great - his coach at South Africa 2010.
"The comparison with Maradona is a very nice compliment, but not one that I can accept yet," Messi said.
"He did so much for the national team - and I don't think any player can be considered a true great until they have won the World Cup.
"I hope that I can do that and I hope I can do that this summer - but until then I don't talk about me as the best."
Maradona led Argentina to World Cup success in Mexico 1986 at the age of 25, while Messi will turn 27 during the latter stages of this summer's showpiece.
The Rosario native has hit an amazing 354 goals in 424 appearances for Barcelona and won 21 trophies at the Catalan club, but believes his achievements should be considered in their true context at the end of his playing career.
"When people say nice things about you and the way you play the game it is always nice to hear - but I have always said when I retire is the time to look back at what I have achieved," he added.
"For now it's about constantly trying to improve and winning things with Barcelona and Argentina."