Demba Ba completed his brace in dubious fashion in the 83rd minute of the clash at the Madejski Stadium, deflecting a Shane Ferguson cross in with his hand as he attempted to head the ball.
 
Newcastle manager Alan Pardew admitted Ba's goal should not have stood and said his team did not deserve their point.
 
McDermott was upset referee Andre Marriner missed what he felt was a clear handball.
 
"It is disappointing to say the least," McDermott said. "I think every angle in the world shows it's a handball. There is no doubt.
 
"We knew at the time on the bench because the ball was going across the goal and he has put his arm out and it has gone in the net.
 
"Whether it was deliberate or not, it's a nailed on handball and in this league you need to get the big decisions right.
 
"It was pretty blatant that one. But he (the referee) hasn't seen it, what can I say?"
 
Ba had earlier cancelled out Jimmy Kebe's 57th-minute opener before Noel Hunt restored Reading's lead with a glancing header just after the hour-mark.
 
Pardew and McDermott worked alongside each other at Reading and the 51-year-old Newcastle manager said the hosts would have been worthy winners.
 
"I have seen it again and it definitely hits Demba's arm. I feel for Brian, he hasn't got the win that perhaps he deserved today," Pardew said.
 
"I am not sure I will say sorry because professionalism won't let me do that but I will say his team deserved to win, I have no problem with that."
 
Pardew said his team needed to improve and added they were lucky to escape with a point.
 
"We have got to find a way of getting rhythm in our play but Reading did a good job of upsetting that today. They didn't give us a moment's piece. They were all over us," he said.
 
"Some good teams will get beaten here and we were fortunate we weren't one of them."