The Belgian international currently has a £23.5m buy-out clause in his Everton contract – but that runs out on August 14. After that date the Toffees can hold out for as much as they want, and with three years left on his Goodison Park contract, Fellaini would be worth at least £30m.
New United boss David Moyes was expected to try to bring Fellaini with him to Old Trafford, but a deal is yet to materialise. But he knows all about the release clause deadline – having negotiated for it while Everton boss two years ago.
And with Bayern Munich now looking the more likely destination for Barcelona starlet Thiago Alcantara, the United manager may turn his attention back to his former player.
Arsenal have also been linked, and reportedly had a enquiry swiftly rebuffed by Everton officials earlier this summer. So far the Gunners have focussed their resources on completing a deal for Real Madrid striker Gonzalo Higuain.
A striker is thought to be their main transfer priority this summer, but Arsene Wenger remains a fan of Fellaini, having watched the Belgian physically dominate his Arsenal sides in the past.
But both Premier League giants are running out of time if they want to make their move. With pre-season tours to Asia getting under way and Fellaini currently at the Everton training camp in Austria, United and Arsenal will have to get organised – and quickly.