Pep Guardiola expects Rodri to be "out for a long time", though Manchester City are still waiting for official confirmation on the extent of the midfielder's injury.
Rodri sustained a serious-looking knee injury during a corner in City's 2-2 draw with Arsenal on Sunday, having turned awkwardly while tiusslinThomas Partey.
The former Atletico Madrid man has since been seen in Barcelona, with reports suggesting that he has suffered an anterior cruciate ligament (ACL) injury.
That would possibly keep him out for the season and would be a huge blow to City, for whom he has proven to be a key man since joining in 2019.
Before City's EFL Cup third-round tie with Watford, which they won 2-1 to progress to the next round, Guardiola was unable to offer any updates on his condition.
However, in his post-match interview, Guardiola conceded that he would be without the Spain international for a prolonged period.
"Rodri will be out for a long time, a while," Guardiola said.
"There are some opinions that it will be less than we thought, but we are waiting for the last phone calls from him and the doctors for what definitely he has and the type of surgery he has to get. We should know tomorrow."
Rodri played 50 times for City in all competitions last season, losing just one of those matches.
However, in the nine they played without him, their win percentage dropped from 76% to 55.6%, with their points-per-game dropping from 2.5 to 1.7.
And Guardiola knows the onus will be on him to find a solution.
"When a team doesn't play with the best midfielder in the world for a long, long time, it is a big blow," Guardiola told reporters.
"Yes, he's irreplaceable. But my duty is to 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."