Henrikh Mkhitaryan has moved closer to sealing a move to Manchester United after a "significantly improved" offer.
"My knee showed no negative reaction. If it stays that way, I'd like to think that I will take part in the first training session," said Boyd.
Wolfsburg forward Andre Schurrle has said he does not want to discuss reports linking him with Borussia Dortmund.
Borussia Monchengladbach forward Raffael has agree a contract extension, keeping him at the club until 2019.
Hertha Berlin are worried that centre-back John Brooks could miss crucial parts of their preseason as they bid to qualify for Europa League.
Douglas Costa has spoken of his affection for Pep Guardiola, the manager who brought him to Bayern Munich and helped him develop as a footballer.