Just saw the decision, what an idiot of a ref... in United vs Villa.
Absolutely cost them a CL spot.
They have a rule in tennis that even if the lineman calls out and the shot goes in and the opponent clearly wouldn't have been able to do much since it is a clear winner the point is awarded. Should be the same in football. Even if a dumb ref whistles but the goal is basically scored a fraction of a second later, the goal should stand.
There's isn't anything United could have done to prevent the goal even if no whistle. None.