A bit off the wall but I'd slot him into midfield and bring Holding in next to Kos.
His best assets is his ability to make crucial interceptions and I reckon he can beef of that midfield.
Also seems to have no problem going forward. Reckon he would relish playing in the role. Get some strength in there and have Ox & Xhaka either side of him for extra support.
something like...
Cech
Bellerin
Holding
Kos
Monreal
Ox
Mustafi
FakeKante
Alexis
Lucas
Welbeck
