Martin O'Neill's reaction to the 4-1 defeat against Benfica has been interesting, to say the least. The Celtic manager seems to have taken it in stride. Perhaps the fans would have wanted him to seem a bit more bothered by the heavy defeat.

This leads one to question how serious the club actually are about their European ambitions. They have lost their first two games of their Europa League campaign and quite convincingly.

The focus now turns towards league competition, where there is no room for error. Celtic's next contest is against a Hearts team that took the title race down to the final day of the previous campaign.

So, there could be an added intensity to this Hearts matchup. And after that, they are set to continue their Europa League campaign against Celta Vigo.

Unfortunately for Celtic, though, it looks like they will be without one of their key players for both these important matches.

While speaking to Sky Sports, O'Neill confirmed that the game against Hibernian next weekend is the earliest he expects Cameron Carter-Vickers to be back available.

So, Carter-Vickers looks set to miss at least the upcoming two games against Hearts and Celta Vigo. And it goes without saying that his absence continues to be felt in this Celtic team.

O'Neill had Dane Murray and Auston Trusty as his centre-back duo for the game against Benfica as Celtic conceded four goals and looked far too easy to go through at times.

Even on paper, a centre-back pairing of Murray and Trusty does not look strong enough. One can only wonder why Liam Scales was left on the bench as an unused substitute.

Perhaps O'Neill wanted a left-right combination with his two centre-backs. If so, Carter-Vickers would most likely have started ahead of Murray if available.

Now, the Hoops have to make sure that they navigate these next two games without Carter-Vickers.

It is not just his quality that Celtic are missing at the moment but his experience as well, as the club try to find their way back into form. They have lost four of their last five games across all competitions.

Interestingly, we have not seen Carter-Vickers in action since his controversial comments about the team needing a script following the defeat against the Rangers before the international break.