McDermott told BBC Berkshire: "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.
"It's important I do the right thing by him as well. For me he'll go down as a very special Reading player."
He added: "Do I want to lose Shane Long? No, absolutely not.
"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."
Long scored 25 goals this season for the Royals in 2010/11, but started slowly, finding the net only four times in his first 19 league appearances.
"He was getting a little bit of stick as well but he's really come good over a period of time," McDermott said.
"I would sign him for any club I ever managed."
The Reading manager also paid tribute to outgoing defender Ivar Ingimarsson who left the club last Thursday after his contract expired.
McDermott said: "It was right for him and it was right for the club. He wants to play week-in week-out and I understand that and the last thing I wanted would have been a frustrated Ivar around the place if he wasn't playing.
"He's done a fantastic job for Reading over a five-year period. Steve Coppell said he was probably his best signing, which is a massive compliment to Ivar.
"So he'll move on with all our best wishes from the players and the staff and all the fans."
Source: BBC Sport
Source: BBC Sport