The 23-year-old Icelandic international signed for Andre-Villas Boas' side this summer after a hugely successful six-month loan spell with Swansea last term.
McDermott believes he will get a positive reception upon his return to Reading, having spent two years between 2008-10 at the club.
"He will get a great welcome. Gylfi never overly wanted to leave, that’s my gut feel," McDermott told the club's official website.
|11/1||Reading are 11/1 with Bet365 to beat Tottenham 2-1 on Sunday
"It was probably the right thing for him, and the club needed that money at that time – so the deal was a good deal for the club.
"He’s such a good guy, we’ve got great relationships with Gylf and his family."
It has been three-and-a-half weeks since Reading last took to the pitch competitively against Chelsea in their 4-2 defeat at Stamford Bridge, but McDermott feels his team are ready for action after coming through a friendly during the international break.
"It’s been such a long time since we’ve played, we had a game in Ireland which was useful for us but we’re ready to get going now,” he said.
"I watched Spurs play against Norwich, but I think the make-up of the team could be different because of the players they’ve brought in.
"We want to be an exciting team to watch, and anyone that watched us at Chelsea would say that we played really, really good football – and certainly should have got a result.
"We want a performance on Sunday, training has been absolutely excellent."