Ok First of all let's get something very clear, you shouldn't even be speaking of sacking your manager, I know this only applies to a few of you so I guess I'm addressing them. With all due respect,
you're not getting a Mourinho or a Hiddink in to manage your side any time soon so you can stop hoping some miracle worker is going to come in and save the day, Martin O'Neill is possibly the best manager you've had or are going to have for a long time. He's proven himself in this league with two sides before coming to Sunderland, taking one of them on regular trips around Europe, the guy knows what he is doing.
You can't just change the manager every time you need a morale boost to your players, you get through the rough patches and you come out of the other end much stronger.
At a guess I'd say you've got some bad blood in the dressing room, amongst some of your players. I'd point the finger at James McClean first and foremost,
then Larsson. I'd guess that the acquisition of Johnson has upset either one or both of them. McClean's antics for his country suggest he thinks he's a lot better than he is, and it's pathetic, the little nugget needs a reality check because I've no idea where his ego has come from, compare his work rate and attitude to Sterling at Liverpool to see my point. Until O'Neill has access to other options in place of these two I'd assume he has to stick with them. I really can't see any other problems in your team as they all seem like top guys, especially O'Shea and Brow

but I will say, Kieran Richardson was a ready made solution for a problem like McClean.