Messi set a new benchmark in Europe when he became the first player to score five goals in the UEFA Champions League during Wednesday's 7-1 win over Bayer Leverkusen.
As a result, the Argentinean has been lauded by pundits and his fellow professionals but that has only fed the fires on the debate as to whether or not Messi is the best of all-time.
However, for Zaldua there is nothing much to argue about. For the 70-year-old, Messi stands head and shoulders above anyone else.
"Messi is the best player I've seen in my life," Zaldua told Sport.
"I've seen Pele, Di Stefano, Maradona and Cruyff but nobody like Messi.
"This ease with which he scores. He does it all so easily; I have not seen anything like it.
"I have not seen anyone like Messi. There is just no end to him. He is a phenomenon, an extraterrestrial.
"He will destroy and kill all the records that we have or might have. He is a marvel."
Barca have now progressed to the quarter-finals at the expense of Leverkusen who were soundly beaten 10-2 on aggregate on the back of Messi's herculean effort.
"I still feel that discussions on whether Messi is the best player in the history of the sport or not, if he can be compared to other players... for me there are no comparisons," Barca president Sandro Rosell said on Thursday morning during a Global Sports Forum session.
"He is the best player ever. I don't think we'll ever see another player like him. Like Guardiola said, let's enjoy him because he's incredible, he stratospheric.
"He's the best player in the world, for Barcelona and for Argentina."
The Argentina international may have notched up 14 goals in his last five matches for club and country, but off the pitch he remains typically reserved.
"The most important thing tonight [Wednesday] is that all these goals we scored take us one step closer to winning the Champions League, which is our objective," Messi told UEFA.com.
"I have always said that it's fantastic when things come off for you like tonight and you play well, but only if you meet your aims for the match. That's what happened against Leverkusen. The team played very, very well, the performance had some beautiful moments and we scored lots of goals.
"It's all about enjoying the moment - from how it went with Argentina the other week [scoring his first hat-trick for the Albiceleste] to how it's going right now for my club.
"The sweetest part of it, for me, is that the team continues its run of form at the moment, winning games in style; that's the way to go as far as we can in the Champions League".
Prior to Wednesday's rout of Leverkusen, Messi had already scored four goals twice in the Champions League before against Valencia and Arsenal.