Celtic might have a pretty big squad at this point in time but they lack is balance in a number of aspects. They need to find the right combination of youth and experience. At the same time, they also need to add quality players who can deliver not only in the Premiership but also in the Champions League.
Celtic's form in the league has been questionable as well. But they have seemed particularly off colour in Europe.
Except for the 2-2 draw against Atletico Madrid at Parkhead, they have lost every other group game so far. And as far as the Champions League goes, the competition was not steep. Feyenoord are a good team but Celtic should be competitive with them. On the other hand, Lazio have struggled all season. The Hoops got two wins over the Italian club, home and away, a few years back in the Europa League when they were in much better form.
Some Celtic players just have not delivered in Europe. On the other hand, it looks like Brendan Rodgers does not believe that David Turnbull has the right attributes for the Champions League.
Rodgers explains why he drops in-form Celtic player in the Champions League
As reported by The Scottish Sun, Rodgers said about Turnbull:
"We’ve got David Turnbull, whose strengths are to play against low blocks when we’re trying to nick a goal.
“Getting around the pitch is maybe not his strength. When you go into Champions League games you need that ability to run. So Paulo Bernardo has played in those games."
Turnbull has done a great job whenever given a chance in the league. He might not be a regular starter when everybody is fit and available, but he certainly has proven that he is more than good enough to be an important squad contributor.
He has not gotten a lot of chances to show that in the Champions League though. He was left on the bench for the first three group stage games and has come on as a substitute in the previous two, but not made much of a positive impact.