Rodri protested at the time, and there was a delay before referee Anthony Taylor’s decision was upheld by VAR, but Guardiola claimed there could be no excuses for his conduct.
The City manager said: “Hopefully Rodri will learn. The game was perfect with 35 minutes gone and after it became chaos.
“That’s not our responsibility, that’s for sure, but Rodri has to control himself and his emotions. I can get a yellow card but Rodri can’t. I don’t play. The guys inside (the pitch) have to be careful.
“I said at half-time, ‘Be careful guys, relax, control your emotions’. Unfortunately, Rodri could not do it. Now we have to accept the decisions.”
Asked if he was angry with Rodri, Guardiola said: “Yes. I don’t like to play with 10 for our faults. He has apologised.”
Despite being critical of Rodri, Guardiola was not happy with the way the game was controlled by Taylor.
As well as Rodri’s red card, there were 11 bookings during the game, including one for Guardiola himself.
Guardiola said: “The referee changed the game.
“For the first 35 minutes, it was absolutely not (a bad game). What changed? What happened after 2-0, it’s not down to us. You have to ask the other ones but I don’t know if they will hang up the phone.”
City had put themselves into a comfortable lead with goals inside the first 14 minutes from Phil Foden and Erling Haaland.
After Rodri’s departure, the hosts needed to change approach and Guardiola was pleased with the outcome.
He said: “Our game in the first 35 minutes was beyond good, how we find our men free, it was really, really good.
“It was a lot of minutes we had to defend, and we conceded one chance in the 94th minute. We didn’t concede anything else, against a team who won at Stamford Bridge and created problems at Arsenal and Old Trafford.
“I’m really satisfied and pleased for all of us.”
Forest manager Steve Cooper had conflicting thoughts about his side’s performance.
He said: “We had a really poor start in terms of goals conceded. We knew the level of the challenge we faced here – it doesn’t get any tougher – and the two City goals were of great quality, typical City goals.
“But we’d planned for that. It was a repeat tactic and to let it happen as easily as they did – if they were going to score I wanted it to be with real difficulty.
“The game changes with the red card. That we had a second half played in City’s half I have mixed feelings about.
“You rarely get an opportunity to have that territory here. Even more experienced teams don’t get anywhere near that but we need to make more of these opportunities. We have got to be more productive.”