There's not much more to say about this beyond the headline, really.
From this, it's pretty obvious something's up with the Brazilian right back, and all the signs seem to be pointing towards a move to Chelsea. I'd expect any news on this front to accelerate in the next few days, as the same source is reporting that Maicon is expected back on the 9th June. I wouldn't go as far as saying this confirms he is definitely in talks with Chelsea however, because there's been a few noises in the past few days about a reunion with Jose Mourinho at Real Madrid, who are also chasing a new right back.
The other explanation here could be that Maicon might just be being really lazy and is not bothered enough to turn up for pre-season training.