Football fans are very quick to bin a player when he doesn't perform. They have no concept or understanding of what else could be going on in a players life.
When a 21 yr old moves abroad abroad nd doesn't speak the language, he can quickly become isolated and alone. I remember Sandro posted a pic on social media early into his Everton career. He was injured and was wishing the team well. The picture was his foot in bandage, in the background was his modest looking flat, with a TV showing the game. The place look sparse and devoid of home comforts. He was living alone in new surroundings without friends or family, his move probably wasn't going to plan...he was seeking reassurances and he got a load of responses slanging off the small size of his tv and his crappy furniture.
Who knows what has gone through his head over the last two seasons.
The club made a huge error offering him such a large salary. And unfortunately he has proven to be a bad investment. But nobody ever seems to consider the external factors foreign players face coming to the PL.