Dusan Vlahovic's effort and a stunning volley from USA international McKennie condemned City to an seventh defeat in their last ten games.
The result leaves City's hopes of qualifying for the Champions League knockout rounds in serious jeopardy.
City are in 22nd place out of the 36-team table where they have picked up just eight points from their opening six games.
Failure to reverse the situation in their final two games against Paris Saint-Germain and Club Brugge could see City prematurely crash out of Europe.
In what began as a season full of promise, Guardiola's men are in the midst of a full-blown crisis, but it appears that not everyone has sympathy for the reigning Premier League champions.
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McKennie, who spent six months on loan at Leeds United in 2023, appeared to brush off any compassion for the Premier League side when asked about their current plight.
Liverpool legend Jamie Carragher commented on his opinion that City are going through a 'big crisis' and asked the American for his thoughts on the Etihad outfit on CBS Sports.
Standing alongside ex-City right-back Micah Richards, McKennie proceeded to laugh off the question.
He then cheekily quipped: "Honestly, it seems he [Richards] should suit back up and go back out if he wants to."
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His response drew fits of laughter from the panel in what could have been construed as a jokey dig at the club's current right-back Kyle Walker, who has struggled for form this season.
However, as per the usual tone of the CBS Sports broadcast, it was all taken in good humour.
The result propelled Juventus up to 14th in the Champions League table, where they look set to at least book a spot in February's play-off round.
Discussing the importance of his side's victory, McKennie said: "It was definitely a big moment for the team with the situation that we've been in.
"We knew it was going to be a difficult game because Man City is a team that's all about possession and they can punish you with one action."
Asked about his superb scissor-kick goal, the 26-year-old joked: "I was falling over!"
He then added: "You've seen it before, I did it also against Barcelona so I've got it in the locker every once in a while."
McKennie also lifted the lid on his ill-fated spell at Elland Road which coincided with the club's relegation to the Championship.
The midfielder was brought in by then boss Jesse Marsch to help boost the Whites' survival hopes, but failed to show his best form during his time at the club.
He said of his time in Yorkshire: "The city itself and the surroundings were a little bit hard.
"It was always grey, I had a sunlight window in my house and there was never any sun coming through. No Sunday roast, no nothing. I was alone.
"My area was like no area, nothing around. I went up to see Harry Potter World which was like an hour away. That's it, that's all I did, and golf."
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McKennie admits that failing to settle in England was among the reasons why he was unsuccessful at the club.
"I will say this, Leeds as a club, the people within the club, I liked," McKennie told CBS Sports panel.
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