Brian McDermott's side were humiliated at Hillsborough in front of a live television audience one week after being outplayed by Sky Bet League Two side Rochdale as they crashed out of the FA Cup.
But the Scotland international believes a crisis meeting on Sunday has helped clear the air and said victory against table-topping Leicester on Saturday was not out of the question.
"Saturday was highly embarrassing," the 27-year-old told the club's official website.
"You can't really say how you feel because it was that bad.
"It felt that bad, I've watched it a couple of times since and it's even worse."
McCormack added: "We had a clear-the-air talk on Sunday morning. A lot of people said their piece and it went well.
"If people don't say how they feel it can fester and sometimes you need a meeting like that.
"We have to take full responsibility. I've spoken to a lot of fans and a lot of people, and people are going on about formations, but formations don't win games - players do.
"We needed that meeting, we need this week, and we need to get back to doing the things that put us within a point of the play-offs.
"We've been working hard on the training ground and we've been looking at videos at where it went wrong.
"We're all professionals and we're paid good money to put on a better show than that.
"We tend to do well against the teams we're not supposed to. Last year Leicester and Palace came at a difficult time and we beat them both in the same week.
"We can beat Leicester, no doubt about it."
- Sports & Recreation