Guardiola was unhappy with the Mitre match ball, which is usually used in Football League matches.
"It is not acceptable. The ball was unacceptable for a high-level competition," the Spaniard said.
"It is too light, it moves all over the place, it is not a good ball. It is impossible to score with a ball like that and I can say that because we won, I'm not making excuses.
"All of my players said, 'What is that?' I'm sorry [but the] Carabao Cup is not a serious ball for a serious competition.
"It's [for] marketing, money, OK but it's not acceptable – [it has] no weight, nothing."
Bravo made saves from Alfred N'Diaye and Conor Coady in the shoot-out, sealing a 4-1 win on penalties for City.