~snip~
Manchester United team is now 9 points behind Aston Villa. However, Manchester United may have a slim chance of finishing in the top four if United's overall performance remains stable. But Manchester United's performance is still weak and erratic. Manchester United have lost two of their last three matches. Such an erratic performance will not be able to close the gap of 9 points with Aston Villa.
Sometimes things like this make it increasingly difficult for Manchester United to shorten the point difference and I quite agree with your statement above that Manchester United has only a small chance of being able to overtake Aston Villa. However, Manchester United is actually in a trend that is not that bad and they could jump further up to disrupt the competition for the top four.
On the other hand, even though Aston Villa is quite comfortable, Spurs also always take advantage of the situation if Aston Villa experiences a deadlock. Of course, Aston Villa will not always be calm with such a difference and for them, not only Manchester United but Spurs will also put pressure on them in the remaining matches this season. So Unai Emery has to be really careful considering that the competition in the English Premier League is so competitive and even at the end of the season the difference is very thin to determine that.