The problem we (united) have right now is that we are simply incapable of going on any meaningful run AND we can't score more than 2 goals a game. Defensively, whilst we have somewhat improved (I would actually put that down to the quality of opposition we have played) we are still likely to concede a goal and everyone knows what happens to this team that has a mentality of a toothpick once we do concede.
We also have the small matter of fact that from March onwards our fixtures get extremely tough, we have to go away to liverpool and city and arsenal. Home to spurs, chelsea. I can genuinely see us loosing all those games. And once we inevitably get knocked out of the CL by Atletico, the players won't give a shit. So all in all, its a tall order for us to get top 4.