Tomato plant is looking sickly...?

It could be a mineral deficiency so try giving a liquid feed that contains potassium such as tomorite. As the leaves are curling it could be aphid or other insect damage so have a look to see if there is any livestock inside the furls. It could be that it needs watering or worse still it could be blight developing as there appear to be some brown spots coming on the leaves. If it is it will develop and you will need to pull up and destroy the plants although some of the fruit will still be ok to eat.

Finally it could just be the end of the season. Tomato plants are annuals and as soon as the temperatures drop at night they start to suffer and as the season draws to a close they will die.

For some reason nutrients are not getting to those leaves. Could be lack of nutrients as already mentioned, try chelated iron and a bit of nitrogen. Is the plant shutting down for season's end? Could also be a disease that has infected the water and food conducting vessels in the plant and is slowly shutting off the flow. Most of your tomato diseases work in this way. Diseases can come from the soil, splashed from water and dirt onto leaves or from an insect feeding on the plant and transferring the disease. Often no cures for diseases in these annual type plants.

Normal, late blight. Pull off bad leaves and trash them.