What's wrong with it?

[Junebug]

Originally Posted by pheli

Thanks all.
Here is an enlarged image. In fact, I am worried about the purples along the vein. The leave is injured due to a typhoon hitting. The other leaves do not have such purple changes. Virus test is also expensive here, so I do not plan to order a test.

It simply sounds like you have one old beat-up, sunburned dying leaf. I wouldn't fret about it. It's normal to have one or two leaves die off every once in a while. You can let nature take it's course or cut it off and treat with cinnamon.