The Owls are thought to have made a £10m bid for the striker back in January and are now prepared to up the ante in their quest to land the 29-year-old who was sold by Leeds United for £11m in July 2014.
Fulham are understood to be willing to sell but value the Scottish international at £12m.
The Cottagers have rarely looked like mounting a promotion bid in the two seasons since McCormack’s arrival but the prolific striker still netted 23 goals last term and 19 in 2014-15.
Wednesday’s current record transfer fee paid is the £5.7m paid for Paolo Di Canio to Celtic in August 1997.
The Owls have also been strongly linked with a move for former Sunderland striker Steven Fletcher and are reportedly closing in on the 29-year-old’s signature.
The forward was released by the Black Cats this summer and has attracted interest from a host of clubs including Norwich City.
Fletcher has also been linked with a move to Celtic but the race for his signature looks between Norwich and Wednesday who have offered the forward a longer contract than the relegated Canaries.
Fletcher, 29, spend the second half of last season on loan at French club Marseille but netted just once in 14 games.
Another name linked with a move to the ambitious Owls is Villarreal defender Bojan Jokic.
The left back is entering the last year of his contract with The Yellow Submarine and spent the second half of last season on loan at Nottingham Forest.
But despite being linked with a whole host of new arrivals, the Owls face a serious battle to keep star centre-back Tom Lees who continues to attract strong interest from Burnley.
The Clarets face their own battle to keep hold of centre-back Michael Keane who is wanted by Premier League champions Leicester City who are being asked to pay around £15m to secure the 23-year-old’s services.