Guthrie's future at Reading looked to be in doubt after he refused to play in Tuesday's 3-0 defeat at Sunderland.
He has been fined and disciplined by the club for his actions which sparked a furious backlash from supporters.
But McDermott is ready to bury the hatchet and throw Guthrie into the fray in next week's televised clash at the Madejski Stadium.
Guthrie has not started a Premier League game since the 1-0 loss at Liverpool on October 20 after falling out of favour and picking up a groin strain.
McDermott explained: "I've never been one to write people off, the past is the past. Some decisions people make aren't great and Danny will have to apologise for what he has done. It was disrespectful to myself, my staff and his team-mates and I won't stand for that.
"I can understand supporters' feelings on the matter, it was a natural reaction. What Danny has to do now is apologise, train well and perform to his best ability when asked to play.
"But when players are not in the side they must support the squad and get right behind them. We need that more than ever right now because results aren't going your way."
And he added: "Danny has played 45 minutes of football in the last month. He is slowly getting back to where he should be.
"When I signed Danny I thought he would be playing regularly. But that hasn't been the case for one reason or another.
"But Danny is no different to anyone else. Sean Morrison didn't play for the first team for two years, Alex McCarthy had to wait for his chance, Nicky Shorey and Ian Harte have been in and out of the team and so have Adam Le Fondre and Alex Pearce, who was player of the year last season.
"There are numerous examples of that and Danny is no different. The most important thing is that players buy into the group mentality. It's the only way we will be successful.
"We've got a real fight on our hands here now and we need everyone pulling in the same direction."
Reading's defeat on Tuesday was their heaviest loss in the Premier League this season and leaves them entrenched in the relegation zone and six points from safety.
Successive defeats by fellow strugglers Southampton and Sunderland in the past week have deepened the sense of crisis at Madejski Stadium.
To make matters worse, McDermott has to deal with an ever-increasing injury list with Alex McCarthy, Jason Roberts, Sean Morrison, Pavel Pogrebnyak, Hal Robson-Kanu, Jem Karacan, Jimmy Kebe and Chris Gunter among the long and short-term casualties.
However, Kebe, Gunter and Robson-Kanu all have a chance of being fit for Arsenal, who make their second visit to the Madejski Stadium this season following their unforgettable 7-5 win in the Capital One Cup, having been 4-0 down.
The Gunners, though, looked vulnerable in defence and were dumped out of the same competition on Tuesday night by a League Two Bradford City side managed by ex-Reading legend Phil Parkinson.
Former Arsenal player McDermott stated: "I spoke with Parky the other week and beating Arsenal on Tuesday was an amazing result for him and for Bradford.
"I'm absolutely delighted for Parky but Monday is a different test in the Premier League.
"Arsenal are a massive club but they're going through a bit of a tough time. However, so are we, it happens to the best.
"But Arsene Wenger is a top manager and a top guy. I had a great conversation with him after the 7-5 game which I really appreciated."