Looks more like a nutrient issue but the light in the pics makes it difficult to tell for sure. What and how often are you feeding it since it is in a container?

Dave

I think it is some kind of environmental damage, more likely some kind of burn.

JMO

Sey

My vote is environmental damage, as Sey suggests.

It is the interveinal chlorosis that caught my attention. Yellowing of the leaves between the veins with the veins remaining green frequently indicates a nutritional imbalance.

Dave

I have burned my tomato plants with fungicide / insecticides before when applying them with the full sun out. This is what it looked like. Have these been recently sprayed?