The Spain international has played alongside the likes of Zlatan Ibrahimovic, Andres Iniesta and Neymar at Camp Nou but he says his Argentine colleague is peerless
The Argentine finished second to Cristiano Ronaldo in the battle for last year's Ballon d'Or, after suffering an injury-hit 2013.
However, when Xavi was asked to name the finest player he has ever shared a pitch with, the World Cup winner offered an unequivocal reply.
"When it comes to striking up an understanding and enjoying your football, you always want to play alongside the very best," the midfielder mused in an interview with Fifa's official website.
"But, in my view, Messi is the greatest player of all time. He’s the best there is."
Meanwhile, Xavi was keen to clarify recent comments he made about the possibility of him finishing his career somewhere other than Camp Nou.
"What I said was more about how demanding it is [at Barca], rather than not wanting to [retire in Catalunya]," he explained.
"On the contrary, I’d love to hang up my boots at Barcelona and stay involved with the club, which I think is the best in the world, for many years. I’ve felt that way since I was a boy and still feel the same today.
"I’d like to still be at Barcelona when I retire, but I know how demanding it is. That’s why I said it’s not my decision: to retire here I’ll have to keep performing at the highest level.
"Let’s hope I can do it, it’s my biggest dream."
Xavi admitted that he is also hoping that Barca can re-establish themselves as the best team in Europe this season, though he is well aware that last season's treble winners, Bayern Munich, are the obvious favourites to win the 2013-14 Champions League.
"But that’s where it comes down to other teams to try and stop them," he mused. "One of them being Barcelona, for example, right?
"I think that we’re still capable of big things in La Liga and in Europe, though clearly Bayern are very strong.
"Last year they won practically everything and this year they’re still on course [to do so again]. They have to be considered among the real favourites to win the Champions League again."