The Royals have yet to win on their return to the top flight but McDermott was more disappointed by last week's performance against Tottenham than any other display so far this season.
After not playing in the Premier League for 25 days, due to their fixture with Sunderland being postponed and the international break, the players finally returned with an abject display in a 3-1 defeat to Spurs on Sunday.
McDermott, 51, revealed everyone in the dressing room was suffering after the match and he does not want that to be the case following any other games this year.
"The last thing we want is to have regrets about a performance, that is the key for me," he said. "Since I have had the job we don't go into blame mode or excuse but we would have had regrets after that.
"There was real disappointment in the dressing room after the Spurs game, we all would have had regrets about that game and that performance.
"After the game and when we are sat in the dressing room at West Brom, as long as each and every one of us knows we have done the best we can we will have no regrets about that, and fundamentally when we are at the top of our game we get results."
The former Woking manager is not one for excuses but he did feel the gap between his side's last two league games was always going to cause a problem.
He said: "It has been a bit difficult, obviously in the Stoke game we got a point, we went to Chelsea and should have got something and then played Spurs and got what we deserved, we know that.
"We never make excuses but we are glad we have had that game, three-and-a-half weeks is a long time without a game, we were hurting after the game against Spurs because we didn't do ourselves justice."
The opening-day draw at home to Stoke is the only point Reading have managed to collect so far and McDermott has acknowledged the difference in class between Premier League sides and those the Berkshire club beat on their way to the npower Championship title last year.
He said: "One thing we are is a difficult side to play against and I don't think we would have been seen as a difficult side to play against with Spurs, I think they had a fairly easy afternoon - which hurts us more than anything really.
"Having said that, we are playing against teams with budgets of millions and millions of pounds - you saw the two finishes from (Jermain) Defoe the other day and that is the difference.
"You have players in this division, world-class players, that make the difference - you have seen that in the Champions League games in the last few days."
But McDermott was also full of praise for his own squad and is confident in the ability of his players to mix it with the bigger teams, starting with the trip to West Brom.
"We have got a fantastic group, our mentality as a group is very, very good," he said.
"We have got players with pace, players that can score goals. We have scored in every game we have been involved in so far so we know what we are about and the strengths of our club and the environment of our club and all we can do now is look forward to out next game."