The Italy international says that Antonio Conte's men have been worked out by opponents and that they need to introduce more variety into their play
The Bianconeri reached the quarter-finals of last season's tournament before being eliminated by eventual winners Bayern Munich, but they are struggling this term, having drawn both of their opening group games, against Copenhagen and Galatasaray.
With a double header to come against Real Madrid, Juventus are now in an unenviable position as they look to reach the knock-out phase and Barzagli is worried that other teams have worked out how to play against the Italian champions.
"It's pretty obvious that we are no longer able to play our own game," the Italy international told Mediaset Premium.
"In recent years, the way a lot of squads play has changed and we are trying to alter our approach a little in order to return to the Juventus of old.
"In Europe, however, it's more difficult because one meets strong squads and they tend to always impose their game on you."
Juve had put themselves in a winning position against Galatasaray having recovered from the shock of conceding a first-half goal to Didier Drogba, with a quick-fire double from Arturo Vidal and Quagliarella putting them 2-1 up late in the game.
However, the Turin giants conceded an almost instanteous equaliser to Umut Bulut, and Barzagli conceded that he should have done better to prevent the goal.
"I'll take a little responsibility for Galatasaray's second goal because, with three minutes to go, I should be more alert and covering better," the centre-half conceded.
"As a defender, I should have told my team-mates to defender deeper and more compact.
"It's unacceptable to concede a goal like that, with four against four, having just scored to go ahead."
Juve now face group leaders Madrid at the Santiago Bernabeu on October 23.