As revealed by Goal, David Moyes' side lodged a £10 million bid for the Italy international back in August, only for De Rossi to reject the chance to move to Old Trafford.
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Roma, meanwhile, are flying high in second spot in Serie A and De Rossi believes his decision to stay put at the Stadio Olimpico has been fully vindicated.
"It was a good thing that I didn't go to Manchester, now I would have committed suicide," he told friends, according to Corriere dello Sport.
"Last summer I didn't feel comfortable, I didn't recognise myself in the relationship with my teammates and with the fans."
Moyes' United have been heavily linked with a move for Everton star Leighton Baines during the January transfer window, with Goal exclusively reporting that the Toffees have placed a £25 million price tag on the full-back.