Manchester United boss Louis van Gaal admits his side could miss out on a top four finish this season.
The Red Devils suffered an unexpected home defeat against West Bromwich Albion on Saturday in a game that saw striker Robin van Persie miss a penalty in the second half.
They have a four-point lead from fifth-placed Liverpool but their remaining fixtures include a home game against in-form Arsenal and a tough away fixture against Hull City.
"Normally, Robin shoots the penalties very good but it was also a good save from the keeper," van Gaal told MUTV.
"You have to give the credit also to the goalkeeper but it was our biggest chance as it was without a lot of bodies in front of you.
"It's also a concern now [a lack of goals] because it's not a coincidence and, in spite of the way we have played against Chelsea, Everton and now against West Bromwich Albion, we have created a lot of chances and still we don't score.
"So you can say, as manager, we were not unlucky in every match. It's also that you have to finish these chances. We have lost three times in a row so it's also in the hands of my players. It is less secure [a top-four place].
"I know what is happening, in the defence, West Brom shall park the bus and they have done that.
"The goalkeeper was fantastic and I think they did not give us sufficient space to score the goals as we have created enough chances to score but still from a difficult situation because a lot of bodies are in front of you.
"The goal was not even a chance – it was a free-kick and it was a deflected free-kick also. It is very unlucky when you see what we have created and how we missed the chances and how they scored.
"It's unbelievable but that is also the beauty of football."