Mosaic virus?

If it's the only affected plant, I'd suspect virus.

And because, some viruses can spread by mechanical means or insects to other plants, I would get rid of it --- put in the trash.

Hello, Sorry to say that I strongly suspect Mosaic virus per the photo. I have continued to grow in the past if it had lots of fruit already set and was near end of season. However, if you still have plenty of growing time, I would toss it and start over in a very different growing area. It can easily spread to others.

thank you all for your feedback. In 30 plus years of growing tomatoes, I've never seen this before. but it did concern me, so I guess out this plant goes, maybe I'll take a shoot from the healthy plant, root it and go from there.