It went on to say Guardiola and his players "struggled to cope with the result and should be "grateful for the luck they had with refereeing again" prompting City to issue a response in a statement on Wednesday.
"They were spared the sending off of Fernandinho, who at the age of 35 is a clear example that money in football counts a lot, but doesn't buy class," the newsletter said.
A spokesman said: "This is not the first time that Porto have reacted badly in circumstances like this.
"On this occasion it is the ill-judged and targeted criticism of some of our individual players and indeed our manager, which we wholly reject.
"In 2012, the last season we encountered them, it was the denial by the club of clear racist behaviour of their fans for which they were investigated and fined. In this context, this latest outburst is almost as surprising as it is disappointing."
Former City player Joleon Lescott also issued a response, tweeting: "Strange reading the statement from Porto, the game looked comfortable to me.
"Annoying part is the racism claim. No racism should be ignored and trying to deflect isn't going to work. Clearly selective memory, I'm sure them receiving a fine for targeting Mario [Balotelli] in 2012 just a memory."
City's goalless draw with Porto was enough to guarantee Guardiola's side will finish top of Group C with a game to spare.
Porto coach Sergio Conceicao said on Tuesday that he, too, would be upset if he was coaching this Manchester City side and didn't win.
Conceicao, who had had a heated exchange with Manchester City boss Pep Guardiola during City's 3-1 home win in their Champions League opener in October, was told that his adversary was visibly upset with his team.
"Was he?" I would be too if I couldn't win with the team and the budget he has," Conceicao said.
Since their defeat to City in October, Porto have not conceded a goal in their last four Champions League games.
"I don't want to sound vain but we have worked hard over the years and we have progressed to the round of 16 three times with me as coach and it has not been during golden times but rather difficult times," he said. "You have to be creative, in telligent, to continue with a history as big as the one that FC Porto has. We must give credit to the players.
"Many of these players are playing Champions League for the first time. They deserve praise. And this has to do with the difficulties.
"Not only Porto, but other teams when facing a team like this one [Manchester City]. Maybe the most expensive team in the history of football. Then it's normal that Fernandinho feels frustrated because they couldn't win against a team with a tenth of the budget they have."