He always seemed like the kind of player who'd burn out rather than fade away to me to be honest. Incredible talent but shitty application, which is why he was working in a shop in his 20s. Remember when he came back to Chelsea in his second season, 20 pound overweight after eating nothing but barbecue for three months? He was late too. When he moved back to Atletico from Chelsea he was similarly a stone overweight and the coaching staff put him on a training bike on the touchline where he had to pedal away while the rest of the team trained on the pitch. They felt shaming him in front of his teammates was the only way to get him back into shape.
I think he's the sort of footballer who'll play out of his skin when he has a point to prove, like he did at Atletico and Chelsea early on, but once he gets comfy he'll train and perform like a Championship midtable player.