It depends. Have you been trying your best during As, because if a U is the result you got after working hard then yes, you may have to drop it.
However, If you know that you've been slacking and you could do well in it, then I suggest you stick it out, and start working harder.
Don't let the fact that your chosen uni will know your result stop you, if in the end you get a good grade you can get in through clearing, or take a gap year and re apply.
(Also if you dislike the subject then drop it)