Need help diagnose death (may contain gory images)

[Eonflux]

As @casportpony , said, lymphoid leukosis, although more common in chickens than in gamebirds.
Looking at the pics of the necropsy, you can see that it had metastasized and it's emaciated appearance was another sign of the disease's progression.
Sorry for your loss!'

I’ll accept that as the cause of death. After doing some reading on the disease , the quail display most of the symptoms I observed. And I don’t doubt that the quail been living with the tumor for a few months