Having impressed for the Italian giants for a number of years, centre-back Koulibaly is allegedly valued at £81m.
However, the Senegal international was powerless to stop the Serie A outfit from succumbing to Barcelona in the Champions League last 16 on Saturday night.
Despite City being heavily linked with an approach for the centre-back, Richards has urged caution, insisting that the highly-regarded 29-year-old showed similarities to previous expensive failure Mangala.
Speaking to CBS Sports, Richards said: "I think his price tag is £20m less. Everyone talks about how he is supposed to be composed on the ball, he's aggressive but I see similarities to Mangala.
"He went to City and it didn't really work out for him there so I'm not totally convinced after that performance."
After City spent £32m on his signature in 2014, Mangala eventually left on a free transfer five years later after making just 79 appearances in all competitions. body check tags ::