The Lions kicked-off the 2011-12 campaign with a point at the Madejski Stadium way back in August, having thrown away a two-goal lead in the final five minutes of a thrilling match.
And while McDermott insists he won't be taking Kenny Jackett's struggling side lightly, he believes he arrives at The Den with a more talented squad than he began the season with.
Reading have won their last five games and sit third in the Championship table.
"There has been progression, we've brought players in which have helped the squad, we've gone on a run of performances where we've got results – there's definitely been progression," McDermott told the club's official website.
"It seems an awful long time ago that we were 2-0 down with ten minutes to go, but we know on their day, especially at home, Millwall are a very, very difficult side to play against.
"I've watched their game against Burnley and they were good value for the win. They could have been more than three up. The support they've got is really good for them and they get behind their team; we know what we're going into and it's going to be a very different game."