United made a bid for the midfielder towards the end of the summer transfer window, according to Roma's coach Rudi Garcia, but it came too late for the club to accept.
"It was a good thing that I didn't go to Manchester, now I would have committed suicide!" he told Corriere dello Sport.
It was unclear whether De Rossi was commenting on United's struggles this season or expressing relief that he was part of a renaissance at Roma that has lifted them to second behind Juventus in Serie A.
"Last summer I didn't feel comfortable, I didn't recognise myself in the relationship with my team-mates and with the fans," the 30 year old said.
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