Could be. I would remove all the yellow leaves and spray with a mixture of 1 tbsp baking soda per 1 gallon of water. I would also fertilize it because that is a pretty good size tomato in a container and it will use up all the nutrients very quickly. Maybe mix a tsp of epsom salt into the fertilizer that way you have covered all your bases.
A tomato that big would do better in a 5 gal container but the bigger a tomato is the easier it is to have transplant shock. I just lost one that I that I should have transplanted sooner and didn't. The biggest challenge you will have is keeping in watered and that why a 5 gal container would be better. If you decide to move it, just place it into the container and add soil around it so that you don't stress it. I would feel really bad if you lost it because you moved it though and it could easily happen.
tomatoes are so finicky that yellowing leaves could mean anything from phosphorus deficiency to "that was a lot of wind yesterday, man". It could also just be shock from being moved from whatever indoor greenhouse they were in. I'd prune them off and give it some good vibes and water.
Be careful with fertilizers. If you load plants on nutrients without providing enough water you could run into the plant trying to push energy into growth without enough fuel to do just that.
It's an early girl. I really just got it because I'm impatient and I wanted to have something to harvest before the rest of my garden starts producing anything delicious. I did get a copper treatment and pruned off the yellow leaves or anything that looked sick and now it doing well. I want to transplant it into a bigger pot but I don't want to shock it either?
I've never really had an issue with transplant shock when moving from one container to another, just on occasion when I've planted them in the ground. It might not be something to worry about.
I moved it to a 5 gallon container and now this plant is producing fruit all with blossom end rot. What a pain this plant has been. Not sure what else to do to fix it. I added calcium. Then I tried epsom salt. I'm lost with it