The 26-year-old made his City debut in October 2005 and racked up 245 appearances for the club, picking up winner's medals for the 2011 FA Cup and 2012 Premier League in the process.
However, a string of injuries and the emergence of Pablo Zabaleta as City's first-choice right-back have limited Richards to just 19 games since the 2012-13 season and he joined Fiorentina on a season-long loan in a bid to get back in action.
With France international Bacary Sagna arriving from Arsenal ahead of the current campaign, Richards has criticised Chilean manager Pellegrini for showing a lack of faith in him.
Richards told The Guardian: "The lowest moment was against Watford (an FA Cup game City came from 2-0 down to win 4-2 last term).
"At half-time we were losing 2-0. I really don't want to pass the blame to other players but everyone could see I wasn't the problem.
"But Pellegrini brought me and [Jack] Rodwell off at half-time.
"I thought: 'I'm becoming a scapegoat here'.
"I've not always played well for City, but I'd never been the scapegoat, coming off at half-time when in my head I thought I was having a decent game.
"It was weird, unnatural, it had never happened to me before and it felt like no matter what I did it wasn"t good enough anymore."
And the England international, who earned the first of his 13 caps at the age of 18, acknowledged that from then on he was no longer confident of continuing his City career.
"That was a turning point," he explained.
"The manager did try to explain it to me - he said he didn't want to rush my fitness, but I wasn't playing in the Premier League, I wasn't playing in the Champions League, so at least, in the FA Cup against Watford at home, give me 90 minutes.
"After that, my belief was shattered."