i think he is healthy or he'd still be on the injured list. he's just still trying to get match fitness and get a feel for the league. Ronny said in his press conferences before that Talles is not as fit as Thiago and it shows. It will just take some time. Both players will need time to get used to the league, but it seems Thiago is adapting faster (which could be due to his better fitness).
Unfortunately, the best way to get match fit is to actually play. So Talles will need to get more minutes if he's ever going to get match fit and give us his full potential. We just have to be patient.