The Royals travel to Old Trafford in the fifth round of the competition on Monday night.
"We have to get the details right," McDermott told Sky Sports News. "The decisions have to go our way and we need to play well and defend well. If all those things come together then we have a chance of getting a result.
"We've got the chance to play Manchester United in the FA Cup with both teams wanting to reach the quarter-finals. It's a great occasion and we can't wait for it."
Reading's previous best in the FA Cup was a semi-final appearance in 1927.