But it is the chance for his father to work in the gardens of Manchester that have helped to swing the deal.
Petrucci said: "Going to play for the strongest club in the world is a great opportunity for me. It was hard to say no, even though I am a Roma fan.
But United have offered my father Stefano a job as a gardener."
Petrucci added: "Now I'll be at the same club as Cristiano Ronaldo. Bloody hell, what a player!"