Brendan Rodgers has explained why Maik Nawrocki and Gustaf Lagerbielke have not been included in recent Celtic squads despite being fit.
The former has not featured for the Scottish champions since August, when he sustained a hamstring injury during the League Cup defeat to Kilmarnock.
While Lagerbielke last played competitively against Livingston in September.
Rodgers said: "It's always personality. There are clearly players ahead of them. What always ticks my attention is training, I'm out there every day watching training and when I see players train and work with that personality they will edge closer to my thinking.
"Unfortunately, for Maik and Gustaf, Scales has come to the team and has really taken his opportunity.
"Nat Phillips has been a great positive influence. It's an area of the team you don't want to change too much."
Meanwhile, Celtic captain Callum McGregor insists manager Brendan Rodgers "gave them character" at half time after their 3-1 victory against St Johnstone.
The Scottish champions started sluggishly and went behind in the first half after a goal-line scramble ended with Diallang Jaiyesimi being credited with the opening strike for the hosts.
However, the Parkhead club improved in the second 45 minutes, with substitutes Mikey Johnston and Oh Hyeon-gyu making an impact.
First, a great strike from the Scotland international brought Brendan Rodgers' men level before an even better finish from Matt O'Riley put the visitors in front.
James Forrest finished the result off with a late goal after a last-gasp save from Joe Hart.
And McGregor was delighted with a turnaround. He told Sky Sports: "We did not do ourselves justice at all in the first half and the manager gave us our character at half time.
"It was nowhere near good enough for a Celtic team and he asked for us a reaction in the second half and we scored three good goals.
"Joe makes a massive save for us at 2-1 and then we go and finish the game off. It was a match of two halves but we produced a really good reaction.
"Once the goal comes, then the place gets a lift, the supporters get a lift and the players just start to move quicker and play with more aggression.
"It was an important goal and there were two other important finishes as well. "
