The former Manchester City man has blasted the recently appointed manager's handling of his goalkeeper.
Joey Barton applauds fans as he is substituted
The England number one hasn't featured in City's opening two games under the Spaniard and his future looks to be heading away from Manchester after 10 years at the club.
And in an interview with TalkSport, Barton, who is now with Scottish Premiership club Rangers, said: "It is not the club I left.
"The club I left and watch now are two totally different organisations. The club I played for wouldn't have treated a player that had been a servant for as long as Joe has in the manner that it has - it is disgusting."
Manchester City's Joe Hart sat on the substitutes bench with Fabian Delph, Gael Clichy, Jesus Navas and Fernando
Hart, 29, has made almost 350 appearances for the Citizens and the outspoken Barton admits he is baffled by the treatment his former teammate is receiving.
Argentine stopper Willy Caballero has been prefered to Hart as Guardiola looks to replace the England stopper before the end of the transfer window.
"I don't see what (Hart) has done wrong to be treated the way he has," Barton continued.
"It is common human decency, regardless of how good a coach you are. Why treat him like that?
"I've watched Caballero and are you telling me Caballero is better with his feet than Joe Hart?
Manchester City's Joe Hart and Willy Caballero during the warm up before the game
"Why not let him fight for his place and then if he is not good enough say: 'I have given him an opportunity'. That's what every manager should do, give everyone an opportunity."
It is clear that the two time Champions League winning manager has concerns over Hart's ability, particularly after his unconvincing display with England at Euro 2016.
And with the arrival of Barcelona's Claudio Bravo supposedly imminent, it would seem that Hart will be left with no choice but to find a new club within the next two weeks.
Manchester City manager Pep Guardiola