Leggo says United are intensifying their pursuit of Marchisio, who has become fed-up with the lack of progress over new contract talks.
The midfielder's camp have been trying to get Juve to reopen negotiations for over a year - but without any luck. Marchisio's €1 million salary is half of Hasan Salihamidzic's and a quarter of Amauri's.
The 25 year-old, a first-choice for Italy, is now exploring his options and has welcomed United's interest.
And it's emerged Arsenal have also made tentative enquiries since United's interest became public.