Celtic lost 2-1 to Aberdeen on Saturday, and the Dons' 1-0 win over Hamilton on Tuesday means that Derek McInnes' men now sit five points clear of Celtic having won every game this season.
The biggest concern for Celtic right now is that, defensively, they look far more vulnerable than they ever did during last season's title-winning campaign.
Last season, Ronny Deila's side conceded just 17 goals in 38 games last season, but in just seven matches this time around, Celtic have already conceded eight goals.
Now, pundit Andy Walker has told Sky Sports that the reason for Celtic's poor defensive showings is that they have lost both Jason Denayer and Virgil van Dijk from last season.
"It will take Celtic time to adjust to the loss of Jason Denayer and Virgil Van Dijk," he said. "They were two extremely accomplished defenders who dovetailed perfectly and they had a good understanding with Craig Gordon.
"The goalkeeper is in poor form at the moment and in general Celtic are struggling to defend cross balls, not only from set pieces but also from open play, and it is something they have to work on and get sorted out quickly," he added.
Denayer was only on a season-long loan deal from Manchester City last term, and has since joined Turkish champions Galatasaray on loan having starred for Celtic last season.
As if losing the Belgian wasn't enough, his partner Van Dijk has also left Celtic, joining Southampton on deadline day in a big-money deal.
Replacements Dedryck Boyata and Jozo Simunovic need time to adjust to life in Scotland and build a partnership in defence, as replacing Denayer and Van Dijk is an unenviable task.