Despite Chelsea undergoing a rather disappointing season, Willian has been one of their few players who has been in good form and Mourinho is reportedly keen on a reunion with the Brazil international.
"I think this lad has been Chelsea's best player this season," Crooks told the BBC.
"Does this mean Paul Pogba or Juan Mata might be surplus to requirements? The bigger question is whether Chelsea would sell another one of their star players to United. 'If so, Antonio Conte might as well give Mourinho the contact details of the company which engraves the Premier League trophy while he's at it."