Leeds rejected a bid from Fulham for the Scotland international last month, but the Cottagers appear to be edging closer to a deal.
Negotiations are ongoing although a fee is yet to be agreed for McCormack, who stayed in England while his team-mates headed off for a pre-season trip to Italy.
Norwich, Derby, West Ham and QPR have also been linked with the 27-year-old after he scored 28 goals for Leeds last season.
United owner Massimo Cellino has suggested that McCormack would only be sold to a ‘big team’, but they are now prepared to let the player join their Championship rivals.
Strike partner Matt Smith admitted he would be devastated if his team-mate departs Elland Road.
He told the Yorkshire Evening Post: “For me, he’s the best player in the division and an absolute magician to play up front with. So I would be devastated if he was to leave as I’d love to have another season with him because I think we are a good foil for each other.”