Richards believes City's defensive frailties need resolving urgently following the seventh league loss of a disappointing title defence and thinks Stones' days at the Etihad Stadium may be numbered.

"The centre-back situation needs sorting because I keep mentioning Fernandinho, in my opinion he's not a centre-back, he's better in midfield, we miss him in midfield," Richards told Sky Sports.

"I don't want to keep mentioning Kompany but I have to because it doesn't look like we've replaced him.

"Stones has won a Premier League. Otamendi has won a Premier League – they were calling him 'The General' only 18 months ago, so I don't know whether he's got to an age where he can't move as well but he's not producing the same performances as a couple of seasons ago.

"Stones has not played as many games as he would like. Has he lost the manager's trust? Probably. It needs sorting."

Stones has been restricted to 10 Premier League starts this season, with his last coming on January 18 in a 2-2 draw with Crystal Palace.

Second-placed City sit 25 points adrift of runaway leaders Liverpool after mistakes either side of half-time from goalkeeper Ederson gifted goals to United pair Anthony Martial and Scott McTominay at Old Trafford.