The news comes after the Royals 3-2 defeat in the play-off final to Swansea City at Wembley and McDermott admits there is nothing his side can do if a team from England's top flight makes an approach.
"If a Premier League club comes in and we decide the deal is right and Shane wants to go there's nothing we can do," McDermott told Skysports.com
"It's important I do the right thing by him as well. For me he'll go down as a very special Reading player."
Long netted 25 times in all competitions last season and has been a regular in the Republic of Ireland national team.
"Do I want to lose Shane Long? No, absolutely not," McDermott added.
"Last season we lost Gylfi Sigurdsson just before the transfer window shut and it took us a while to get over that - 12 or so games."