Noel Hunt poked Reading in front from close range in the 15th minute before Troy Deeney earned his team a point with a 40th-minute equaliser. although the Royals felt they were denied a clear penalty in the second half.
McDermott said: "We're disappointed we haven't come away with the win. We felt we should have won the game.
"We've had opportunities to win and with half hour to go we thought there was only one winner.
"The referee's missed a stonewall penalty when Shane Long was cleaned out [by goalkeeper Scott Loach], which I couldn't understand, but there you go.
"He [Loach] came for the ball, he missed it, caught Shane and then he got the ball - he cleaned him out. If you have something like that outside the box, it's a free-kick, absolute certainty."