O'Neil said: "I take full responsibility for everything that happens and what I'm giving you isn't excuses, it's just where we are. We gave everything to get to this point, we gave everything again today. Some of my shuffling around helped, some of my shuffling around cost us.
"The players gave everything, the fans gave everything and obviously is going to be devastated with the result for the next few days. We're going to have to find a way to dust ourselves down because the Premier League is going to be really tough now, what we're going to have to do with the players we have missing is going to be a real test of everybody. We need to be ready."
Asked if Coventry's first goal was given incorrectly, he said: "I have to answer the questions, it sounds like excuses but it's not. It's not inconclusive, the ball hits his hand then goes in. My bench were pretty clear on that fairly early. It's maybe hit his hand and gone in the goal, VAR have decided they can't see it clearly enough. It's not the reason we lost the game. Disappointed, but more disappointed with the fact that we didn't raise it enough to get through.
"We can move things around, we can play Mario higher but we lose him lower, we play Rayan higher, but we lose him lower. We can move stuff around and we will try and find solutions. We've found a few this season in general. I'm gutted I've not found one today. I'm really disappointed, devastated for fans and players."