The doctors job for Spain is to get him out on the pitch and performing if he can.
That is the reality.
Even if it is wrong for Barca.
The players absolutely have a big say whether can play or not.
I think this is overly simplified.
If it was a WC, sure thing. If not then no, the job of the doctors/physios is to take care of the athletes' health and not only care about their performance, luckily most of the time go hand in hand as enhancing their health will help them perform.
In this particular situation, WC qualifiers that Spain won convincingly, I understand Flick's anger.
De La fuente has a history of doing this now, absolutely running Pedri into the ground first at the olympics, and then playing a visibly exhausted and very young Gavi in a meaningless game.
Also as a physio, I would never put the responsinbility on a 18 year old player, no matter how big a superstar he is.
It's Lamine's responsibility to report the pain and tell how he feels sure, but he obviously doesn't have the medical expertise to examine or know wether that pain could be a sign of a significant injury or not.
The Spanish NT staff was clearly aware of the pain, hence giving him pain killers and not letting him train. If they deem it too serious for him to train, then there's no excuse to play him unless it's an incredibly important match worth risking your health for. It wasn't.
Rumours are vague, but only that it's pain from the pubic bone. I've got no way of knowing whats up with him, but most groin injuries aren't easy to deal with. And given his age, I'd be catious with that area in particular knowing that's when the growth plates of the pubic bone are open (14-20 approx., with most injuries happening at 16-18).
Anyways, fuck De La Fuente and the Spanish NT, they should treat their young players better.