The Argentina forward was at his stunning best on Wednesday, scoring twice in Barca's 3-0 success over Bayern Munich in the first leg of their Champions League semi-final.
That double included a wonderful individual goal that helped put his side on the verge of reaching the final, with Sociedad next up in La Liga on Saturday.
Moyes' side have already beaten Barca this term, but, as the Scot targets a famous double, he waxed lyrical about Messi's talents.
"No-one can defend against Messi," the former Manchester United boss said.
"He may have the odd off day, but he's one of the best players of all time. Teams try and stop him but he carries on, makes no fuss.
"I admire Messi for what he represents, his fantastic football and the fact that he doesn't dive or fake injury - things that repulse me in the world of football."
Barca lead rivals Real Madrid by two points at the summit going into the final three games of the campaign.
With Luis Enrique on course for a treble in his first season at the helm, Moyes added: "They have a great team aside from Messi and can call on the likes of Neymar, [Andres] Iniesta and Xavi.
"I have nothing but admiration for Iniesta and Xavi, two of the finest players in the past decade.
"But we will travel to Barcelona with that intention [of winning again] but we are also realistic enough to know that Barcelona are one of the best teams in the world.
"We hope to put on a good performance and hope to secure a positive result."
