The 28-year-old limped off injured in the 21st minute of the Citizens' 2-2 Premier League draw with Arsenal the Etihad Stadium on Sunday after jarring his knee following an innocuous coming-together with Thomas Partey at a corner.
Man City released a statement on Wednesday confirming that Rodri has suffered a ligament injury to his right knee after undergoing medical tests in Barcelona, and 'assessment would remain ongoing to ascertain the full extent of the injury and expected prognosis.'
Guardiola revealed on Tuesday night after Man City's EFL Cup third-round win over Watford that Rodri requires surgery and will be out for "a long, long time".
The Catalan coach has since provided a fresh update on the midfielder's situation, confirming that he underwent surgery on Friday morning and will not be available again until next season.
Guardiola: 'We got the worst news possible on Rodri injury'
Speaking at a press conference on Friday ahead of Saturday's Premier League trip to Newcastle United, Guardiola said: "He had surgery this morning - ACL and some meniscus, so next season he will be here. This season is over.
"We got the worst [news possible] but it is what it is. Sometimes, unfortunately it happens. We are there to support him. Good recovery, step by step and we move forward."
Guardiola was asked about his comments on Rodri being "irreplaceable" and added: "What he gives us we don't have a similar player, but the other players all together can replace what Rodri has given us since he arrived to us.
"We have to do it as a team and find a way to play during a lot of months without an important player for us. Everybody knows it. Speedy recovery and next season he will compete against them.
Rodri ruled out for eight to nine months with ACL injury
"If we win, yes! If we don't win, it is because we miss Rodri," Guardiola continued. "There is not one day in the last years I was not confident.
"We are stronger with him, we're stronger with Nathan Ake, we are strong with Oscar Bobb. All the injuries we did not want it, but football happens.
"Rodri will be out for a period, not just eight, nine months. As a club we have magnificent players, we will find a solution and it is what it is."
Commenting on whether Rodri's injury is linked to the one he sustained while on international duty with Spain, Guardiola said: "I am not a doctor. I don't know. Nobody knows.
"I have an opinion on that but the international team wanted to do the best for him. It is not absolutely related to the international team."
Guardiola refuses to rule out January move for Rodri replacement
Guardiola was also asked about whether Man City will be forced to enter the January transfer market to replace Rodri, and he replied: "We will talk, we will see what is going on. We have time to see.
"Mateo Kovacic [who played the first four games when Rodri was absent] and I have a few more. Ilkay Gundogan can play in that position, John Stones have too. We have alternatives."
The Citizens were linked with recruiting a new holding midfielder in the summer to provide backup or competition for Rodri, but they opted to bring back all-round midfielder Gundogan on a free transfer from Barcelona, while winger Savinho was their only other first-team signing.
Newcastle's Bruno Guimaraes is one name who has regularly been linked with a possible big-money move to the Etihad Stadium, while Crystal Palace's Adam Wharton and Bayern Munich's Joshua Kimmich are also believed to be among those on their radar.
The news of Rodri's injury "could be a season-changing blow" for Guardiola's side according to Man City expert Steven McInerney from Esteemed Kompany, while former Rangers striker Ally McCoist believes that the Spaniard's injury could end up costing the Citizens the Premier League title this season.
Man City, who are set to battle with both Arsenal and Liverpool for the Premier League title, have not lost any of their last 52 top-flight games in which Rodri has featured; only ex-Arsenal defender Sol Campbell (56) has ever enjoyed a longer unbeaten run in the division's history.
Rodri has made a total of 260 appearances for Man City in all competitions since joining in 2019 and has won 11 trophies, including four consecutive Premier League titles and one Champions League.