Naby is a good player, but he just can't stay healthy enough to be relied upon. Klopp's style does not suit him well, he simply isn't durable enough to play like a mad man for 90 minutes for multiple games. I remember watching him in his first handful of appearances thinking he was worthy of Stevie G's #8. There have even been a few 5 or 6 game runs where he looks really good....then BAM...injury. He can't really get in a groove or develop any real consistency with the rest of the squad. Just not the player we need.
I honestly think Klopp et al, have lost the focus on what made his teams work. He keeps looking for tactical players...he needs a durable beast in the middle of the park. Gini had really good control, but his strength was actually his raw athleticism. He rarely made "technical" passes and often made simple side or back passes. His style brought plenty of ire from people who didn't understand his true worth: ball recovery and retention.
Without Gini (or a player like him), we simply can't win enough 50/50 balls in the middle of the field to justify our press.