The England stopper has been under close scrutiny following a series of high-profile blunders, but his colleagues still believe that he is world class.
"I think it's [Manuel] Neuer, Joe Hart and maybe Hugo Lloris, because I play with him in the national team, then [Gianluigi] Buffon too," Sky Sports News quotes Nasri as saying.
"[Iker] Casillas doesn't play anymore but for me Joe is in the world's top five, easily. I am not worried about him. For the first time in a long time England have a world-class goalkeeper."
Hart was criticised for his performance during City's 3-1 defeat to Bayern Munich in the Champions League midweek, but Richards insists that the whole team was to blame for the result.
"Me and Joe are very close and we all make mistakes. He will bounce back because he is a strong character," he said.
"He is not to blame for the result, the team were not good enough in all areas. He will bounce back.
"He is still England's best keeper. I know we have some real good talents but he is definitely the best. He knows he could have done better with the first [goal], but he will get over it."
City take on Everton in the Premier League this weekend.