The four-time Ballon d'Or winner has become "bored after 15 years of marriage to the game", according to his fellow Argentine
The 67-year-old Argentine, who worked at Camp Nou under Cesar Luis Menotti in the 1980s, claims that his compatriot's performance in Saturday's 3-2 defeat at home to Valencia offered the clearest evidence yet that the Blaugrana No.10 has fallen out of love with the game.
Cappa felt that Messi seemed slightly more motivated in Wednesday night's Copa del Rey win over Real Sociedad but nevertheless maintains that the 26-year-old attacker is these days a shadow of the player who claimed four successive Ballon d'Or awards.
“To play football you need boundless passion, like Messi had, like the great players like [Diego] Maradona ... any important player in the Primera Division: Xavi, Iniesta, Busquets,” Cappa told La Xarxa.
“You need enormous passion, you need that energy that comes from an absolute love of the game.
"[On Wednesday against Sociedad], he participated [in the game] a little more, but the day they played Valencia, I couldn’t understand how a player could play football so dispassionately.
"And especially him, because if we look at a game of his from three or four years ago, there was that craziness, that passion that he had for playing.
"And I don’t know why or for what reason, but that is coming to an end."
Cappa says, though, that it is obvious that the drive that turned Messi into a superstar of world football is now conspicuous by its absence.
“That love of the game, that passion that makes him go and look for the ball on the left, on the right, in the middle, take players on, beat one, then two ... I see Messi has lost that,” the 67-year-old declared.
"He has extraordinary quality, he’s wonderful and at any moment he can come up with a wonderful play, but it’s as if he has been married for 15 years to football and got bored of it.”
Cappa also suggested that Messi's malaise is merely the result of grander problems at Camp Nou.
“I’m talking about Messi, but Barcelona have also lost that passion," he argued. "Before, you couldn’t miss even a second of the 90 minutes because there was always something.
"Now Barca have the ball, sure, and they do things now and again, but they have also lost that boundless enthusiasm they had before.”