You'll probably get a surprise when you check how little minutes he's had.
Dortmund have a different philosophy than Chelsea, unfortunately. Dortmund are all about signing young players, maximising their value and then selling them on. Rinse and repeat. Chelsea it's about signing big, winning trophies and if you can't do that then you're out. It's probably better looking at what he did at PSG and I speak of no knowledge of how he treated youth there. The core principles with the owners seem to be the same though.
I'd love to see him get more of a look in. I just don't see it happening. Desperate to be wrong though.