Probably simply working on pre-season fitnessI thought it was interesting in the video the club put out of him walking around at the club that he met with Welbeck. The rest of the players aren't back until, what, next week, I think. So why's Danny so keen? Not that that's a bad thing.
To start an unfounded rumor, maybe they are thinking about Danny for some kind of coaching role in addition to playing duties? Or perhaps they asked him to come in early since they see him as a leader amongst the players (and with Dunk currently warming the bench in Germany)?