He’s been Wengered. Same thing that’s happened to Bellerin, Chambers, Holding and others. The team is not a healthy place for a young player to keep pushing himself, improving technically, learning tactics and maturing as a young man with the arm a learned winner around his shoulder. He’s surrounded by losers, invalids, no-talent-ass-clowns, and rats looking to bail out. It’s not an ideal environment to build young stars.
Contrast with Cesc. He walked into a team with Vieira and Gilberto to teach him to man a midfield, Bergamp to teach him how to pick a pass, and Pires to teach how to be wily. It is no coincidence he accelerated into one of England’s best midfielders as a teenager