Thinking about it, I understand the decision to let him go for a small fee.
- He is on big wages, which help for the ffp, especially if he leaves with a fee, which will be purely a profit since he came for free.
- He is a year older
- He is usually injury prone and it was a miracle, that he could play the last season without big injuries. Just look at his recent past.
- The club still has 4 CBs (Cubarsi, Araujo, Christensen, Garcia)
The only con I see is, that he makes a good pair with Cubarsi and perfectly executes Flick's demands on the high defense line. But I trust Christensen to do it too and Araujo we need to wait how the pre-season helped him here.
It's a bit risky, but I think this is a case where the club would sell a player at the perfect opportunity, instead of holding on to him for longer than necessary and lose money.