Spots on cucumber leaves
This looks like anthracnose, which is a type of disease. It is not as concerning as other diseases (like bacterial wilt) as you can still produce, pick and use the fruits that come for a while.
It will continue to worsen, dependent on the disease load, weather, and air flow.
Here is our page on cucumbers, including the problems they can have: http://extension.umd.edu/growit/vegetable-profiles-cucumbers
And our page on anthracnose, http://extension.umd.edu/hgic/anthracnose-vegetables
When planting in the future, it is recommended you look for cuke varieties that have been bred with disease resistance. Those can be found listed in this Cornell Extension publication:http://vegetablemdonline.ppath.cornell.edu/Tables/TableList.htm