Midfield is a real mess at the moment. Without KDB and Stones, we’ve only got Rodri and Bernardo. And they’re both already being run into the ground because Phillips, Kovacic and Nunes aren’t good enough to be starting proper matches.
We’ve got no-one who can replace Stones in his role. Akanji is game but nowhere close to Stones’s level - technically, tactically, positionally or as a defender. Pep obviously doesn’t think Lewis coming inside from fullback is a viable option, for whatever reason. But we can’t keep leaving Rodri stood on his own with acres of space all around him - especially if we’re going to continue picking 3/4 players liable to lose balls and create turnovers.
If Stones is still unfit, and Lewis isn’t considered, then the only real option is to sit another midfielder alongside Rodri (Bernardo, maybe Kovacic who might be ok with Rodri holding his hand). But the problem then is that we wouldn’t have any attacking threat from fullback either, so we’d end up effectively with a 6/4 defensive/attacking split, which would diminish us going forward. No easy fix.