Blues were given a mountain to climb after conceding three times in the first 32 minutes.
Although they staged a comeback and scored twice themselves, they ultimately left St. Andrew’s empty-handed.
“To concede three goals at home and in the manner in which we did it is not acceptable to anybody.” said McDermott.
“But we did show a bit of character and could easily have got a penalty just before half time, and it was a penalty, and that would have made it 3-2. Then we scored straight after half time and could maybe have taken something out the game. But you can’t expect to score four goals to win a game, it’s not good enough.”
The first two of Hull’s goals came in a similar fashion and were converted by former Blues striker Sone Aluko.
McDermott said a lot of time had been spent on trying to counteract their attacking threat, but it failed.
“The players were told about it,” he said. “They were shown videos of how Hull play and the manager spoke to them at length yesterday morning and showed them what they should be doing, but perhaps they didn’t take heed or it was good play from them.
“They weren’t spectacular goals; they were just bang average goals really. Our four defenders today are very experienced. It didn’t happen for them today but they’re experienced enough to know how to put it right again and I’m sure they will.
“We’d had a warning just before they scored with exactly the same thing and the goalkeeper Butland made a great save and then five minutes later they go and score.
“What can you say? It’s difficult and a bitter pill to swallow. We’re all hurting at the minute but we’ll put it right. It will be right in time but you’ve just got to be patient with us.”
Blues’ Achilles heel this season has been their home form.
“We’re up and down all the time,” added McDermott. “Our away form has been decent and there have been a lot of good performances. But for some reason some of the players have a mental block playing at home. And I don’t know why because the fans in my opinion have been fantastic and very good. They could easily have gone for them. Yes, of course they are upset, but that happens. It must have been painful to watch when you’re 3-0 down but they stuck with us. On another day we might have got back to 3-3 but you can’t keep giving teams a goal start, never mind a three goal start.”