Gooseberry with Yellow Leaves and Brown Spots. What is it?

[CatflapSquirrlie]

Hi All,

I'm new to this forum so apologies if this has already been asked before.

I have a red gooseberry bush that is in a pot. It's been healthy and growing well but all of a sudden last week some of the leaves turned yellow with brown spots on them.
The other leaves are green and appear healthy. Any ideas of what it could be? This is the first gooseberry bush I've planted.

Thanks