Celtic have been long-term admirers of the 25-times capped Fletcher, who cost £12.5million from Wolves three-and-a-half years ago, and were interested before the start of the season.
The 27-year-old frontman has been on loan at Hillsborough from Norwich City since October and his deal expires on Sunday.
Ex-Carrow Road boss Chris Hughton paid £5million for Hooper when he lured him from Parkhead in July 2013, but his successor Alex Neil has snubbed the player this season.
The Englishman, who cost £2.4million when he joined the Hoops from Scunthorpe United in July 2010 and scored 63 league goals in 95 appearances, has been linked with a return to the champions.
However, his wage demands of £32,000-per-week will scupper any chance of a move back to Scotland.
Wednesday’s Portuguese Head Coach Carlos Carvahal is pondering making the move permanent, but realises he will have to meet the East Anglian side’s asking price.
Hooper doubled his goal tally from 18 games with the Owls when he netted a double in his side’s 3-2 win over Bolton in midweek to send Neil Lennon’s team plummeting to the foot of the Championship, three points adrift of second bottom Charlton.