After enjoying a club-record 32-game unbeaten league run dating back to December 2023, the reigning Premier League champions suffered their first top-flight loss of the campaign at the Vitality Stadium and the first in their history against the Cherries.
A late strike from Josko Gvardiol gave City hope of a comeback, but earlier goals from Antoine Semenyo and Evanilson ultimately secured maximum points for Bournemouth and condemned Guardiola's team to their second defeat in the space of just four days after also losing 2-1 at Tottenham Hotspur in the EFL Cup on Wednesday.
Both Stones and Dias started in the defeat at Spurs, but the defensive duo were left out of the matchday squad for the clash with Bournemouth due to injury, with Guardiola revealing prior to kickoff that both players "are out for a little bit of a long time".
The Catalan coach has since provided a fresh update on Stones and Dias after the match, confirming that the Citizens pair are set for spells on the sidelines.
Guardiola issues Stones, Dias injury update
Speaking to at his post-match press conference, Guardiola said: "[Stones and Dias] are injured. Ruben until the international break will be injured. John - I don't know if he'll be back for the next two games."
Commenting on the rest of his defensive options, Guardiola added: "I'm really pleased for the incredible effort from Nathan [Ake], I asked him this morning and I asked him. He said he wanted to try. Struggle this season with problem in his feet."
"[Manuel Akanji] couldn't play against Spurs and make an effort today. [Kyle] Walker - his last game played was with the national team to reach 100 games and since then could not train one session, yesterday he did six minutes. Rico [Lewis], [has played] a lot of minutes, he was tired.
"We have players with rhythm, but we have other players with a lack of rhythm. It is what it is. Accept it."
What Man City games are Stones, Dias set to miss?
Confirmation of injuries to Stones and Dias means they are both set to miss Man City's Champions League trip to Sporting Lisbon next Tuesday and next weekend's Premier League clash with Brighton & Hove Albion before the international break.
Man City will hope that Stones and Dias have recovered in time for a Premier League home encounter with Tottenham Hotspur after the international break on November 23.
Man City receive triple injury boost, but still down to bare bones
Both Stones and Dias will now join long-term absentees Rodri (ACL) and Oscar Bobb (leg fracture) in the treatment room - Rodri is sidelined for the rest of the season, while Bobb is targeting a return between January and February.
Jack Grealish is also out at present and has missed City's last four games in all competitions with an unspecified injury, and it remains to be seen whether he will be fit to return before the international break.
On a positive note, Man City welcomed back three players from injury against Bournemouth, including captain Walker, who was named in the starting lineup after missing four matches with a knee injury.
Guardiola commended the "incredible effort" of the 34-year-old against the Cherries considering he had not trained for 19 days before starting the match.
Belgian duo Kevin De Bruyne and Jeremy Doku also returned to the matchday squad; the former watched on as an unused substitute after nine games out with a groin problem, while the latter came on for the final five minutes plus stoppage time after missing three games with an unspecified issue.
Meanwhile, Savinho was passed fit to make the matchday squad but only watched on as an unused substitute after being stretchered off with a "strong knock" to his ankle in the midweek loss to Spurs.
Man City have slipped off the top of the Premier League table and now sit in second place after Liverpool came from behind to beat Brighton 2-1 at Anfield, moving them two points clear at the summit.