Photinia Red Robin (looking unwell)

I have three of these but one (which is on a different side of the garden to the other two) is looking very sickly, the leaves have shrivelled up. Is there anything I can give it to perk it up? The other two are fine. tia

 

Hi,

You need to tell us a bit more about them eg when were they planted, recently ? and its the shrivelled one in a very different situation, such as shadier etc.

How tall are they now as there are several versions of Red Robin, some small some large.

 

@ricky101. It has been in situ for years, it is planted on the south side of the garden whereas the others are on the north side. It does not get as much sun as the others but is by no means in deep shade.

 

There's a good chance you'll get some more replies if you could provide some photos.
One of the whole tree showing where it is in your garden and a close-up of the problematic leaves.

This article may give some clues though-
How to Grow Photinia | BBC Gardeners World Magazine.