I have a friend, Burmese, who is training for his first Lethwei fight. He's done kyokushin karate matches before and a street boxing match against a very easy opponent. His fight will be what they call semi-professional lethwei, 5 rounds 3 minutes, all weapons allowed including headbutts but instead of no gloves they'll wear MMA gloves. KO or draw.
About a week before his fight he did sparring and my teacher, who I know to be very very controlled and can go hard without causing damage, kicked him in the head. My teacher is 63 kg and around 175cm tall and my friend 185cm and 78kg and will fight open weight (possibly against a muscular tall 100kg dude).
My friend told me the kick hurt extremely much and he almost lost consciousness. I wasn't there to see it but my teacher, who of course apologized, said he didn't use any force. And the rest of the gym pretty much laughed and said it wasn't a big deal.
The thing is I saw a photo of my friend's face and he had like a dent in his cheekbone from the kick. He also said he had a lot of pain and felt dizzy for two days. But his teachers and gym mates tell him to stop making a deal about it, if he wants to fight he needs to be able to take some pain.
I dont really know how tough this guy is. But he's done heavy hard sparring before. And I know my teacher's body is incredibly hard (they don't kick banana trees in Myanmar, they kick, elbow and headbutt coconuts open) but he is a controlled person so there's the possibility of my friend being sensitive.
But to me this situation sounds absolutely reckless, especially so short before what will be a very tough fight. And I suspect due to a lack of knowledge about head injuries they ignore his worry.
I know this is not directly related to muay thai but I'm asking from the perspective of general safety and fighting. I believe everyone should respect martial art traditions and listen to your teacher. But at the same time your own safety has to be your responsibility and priority.