After taking charge of the Blaugrana following a stint in charge of Barca B, Guardiola evolved the club into the greatest side in Europe and one of the greatest ever seen, with them winning two Champions League tournaments in 2009 and 2011.
He implemented his preferred 'tiki-taka' system of playing, which allowed Barca to sweep away all before them in the four years he was in charge.
However, he has not been able to replicate the European success at either Bayern or Manchester City, being knocked out three times a the semi-final stage with the former and not progressing past the quarters with the latter.
Magath reckons that the success at Barca can be attributed therefore to the brilliance of Messi, rather than Guardiola's prowess as a coach.
"Messi won the titles, not Guardiola," the German told Sport Bild.
"Without Messi, this system has never worked as successfully for Guardiola, otherwise he would have won the Champions League with Bayern or Manchester City long ago.
"Tiki-taka only works if you have players who are technically superior to their opponents. For the spectator, holding the ball, as I call it, is just boring and a top team doesn't really need it.
"In my opinion, Guardiola generally too often gets lost in trying to win a game in advance. That tactic often ends in wrong decisions, which prevent success."
In last season's Champions League mini-tournament in Lisbon, City were eliminated at the quarter-final stage by Lyon.