My female pantha went 4/5 weeks on hunger strike, dropped so much weight. Vet told us to force feed untill she was better, she got dehydrated weak etc . She's been eating for 9 days now and she's gained 4 grams.
In my own personal opinion ( I'm not a professional ) start weighing ur pantha every 3/4 days keep hydrated and offer a different variety of good nutritious food ( calci worms, silk worms etc, he might be bored!!!
I cracked our hunger strike with medium crickets , prior force fed wax worms to get some weight on her .
Good luck with ur buddy -