Named player of the tournament at Euro 2024 as he helped Spain lift the trophy, Rodri played a key role in helping City win a fourth consecutive Premier League title last season.
He has lost just one match for club or country in the past 18 months, also winning the Uefa Super Cup and Club World Cup with City last season.
Since joining from Atletico Madrid in 2019, City have lost just 11% of the matches in which Rodri has featured, compared with 24% without the Spaniard.
“When a team doesn’t play with the best midfielder in the world for a long, long time, it is a big blow,” said Guardiola.
“Yes, he’s irreplaceable. But I will find a solution. There is an alternative, we will do it. When you have one player who is irreplaceable, as a team we have to find a solution.”
This month Rodri said winning the Ballon d’Or – awarded to the world’s best player – would be “a dream”.
He played 63 times for City and Spain last season, and after missing the start of this campaign with a hamstring injury returned against Brentford two weeks ago.
Rodri claimed players are “close to” striking over an increase in the number of games in the calendar, with a new Champions League format adding at least two extra matches before the knockout stage, and the Club World Cup expanding to 32 teams.