The Italy international rejected a switch to Old Trafford in the summer and is adamant he made the right decision, with Roma challenging Juventus for the Serie A title
As revealed by Goal, David Moyes' side lodged a 10 million pound bid for the Italy international back in August, only for De Rossi to reject the chance to move to Old Trafford.
United has struggled domestically in the 2013-14 campaign, languishing in seventh place in the Premier League table, with Wednesday's 2-1 defeat at home to Tottenham leaving the club 11 points behind current leader Arsenal.
Roma, meanwhile, is 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 recognize myself in the relationship with my teammates and with the fans."
Moyes' United has 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 pound price tag on the full-back.