Messi has just returned from an injury which kept him out of action for two months and hasn't quite rediscovered the dazzling form that won him four Ballon d'Or's in a row between 2009-2012.
Barcelona slipped three points behind Atletico Madrid at the top of the Liga table after losing at home to Valencia last weekend, and have won just one of their last four matches in the Spanish League.
That has prompted Cappa, who worked at Camp Nou under Cesar Luis Menotti in the 1980s, to question Messi's current dedication.
"To play football you need boundless passion, like Messi had, like the great players like Maradona ... any important player in the Primer Division: Xavi, Iniesta, Busquets," he told La Xarxa
"You need enormous passion, you need that energy that comes from an absolute love of the game… 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.
"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,
"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."