The 38-year-old credits Dr Steve Peters for reinvigorating his love for the sport and helping him produce the form which won consecutive World Championships in 2012 and 2013
Peters, who has previously worked with the phenomenally successful British Cycling team, has been enlisted by Roy Hodgson to help the England squad with their preparations for this summer's World Cup in Brazil.
O'Sullivan, widely regarded as the most talented snooker player ever, cites his work with Peters as key to reinvigorating his love for the sport and helping him produce the spectacular form which helped him win consecutive World Championships in 2012 and 2013.
And the 38-year-old believes Peters would also be capable of bringing the glory days back to United, who are enduring a torrid season under David Moyes.
"Best signing Man Utd can make is Steve Peters," O'Sullivan tweeted. "They will win the league again. Got no doubt."
Peters' stellar reputation has been further boosted by Liverpool's surprise Premier League title charge this season and the personal endorsement of Reds captain Steven Gerrard.
And O'Sullivan added: "He's working miracles at Liverpool mans a genius. Never worked with some one so good and skillful.."