Brendan Rodgers has stressed that Celtic’s unbreakable spirit can help them defy the odds in the Champions League.

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Rodgers admitted his side have not been at their best so far this season and they have ongoing issues in central defence ahead of Tuesday’s Group E opener against Feyenoord in Rotterdam.

Nat Phillips is a doubt with an ankle issue, while Cameron Carter-Vickers, Maik Nawrocki and Stephen Welsh are all ruled out, leaving Liam Scales and recent signing Gustaf Lagerbielke as the only two definite options for Rodgers.

Celtic are the group outsiders behind Atletico Madrid, Lazio and the Dutch champions but Rodgers is targeting progression of some sort and possibly in the Champions League.

“I think success for us as a club is to be in Europe after Christmas,” he said. “That is what our aim is. Whatever competition that is in, as long as we are in Europe after Christmas, that is our aim.

“But anything is possible in the group. We look to be competitive in all the games.

“I think it’s one where anything is possible.

“People ask you to forecast what it is you want to do and what you want to achieve but I think that how we want the play the game with our competitive spirit, that’s important in the Champions League because you are playing against top teams.

“We have seen already this season that the spirit of this team will never be broken.

“You have to have that at this level when you are a team like ourselves coming into it, when people want to dismiss you in the tournament.

“It’s about being competitive, you have to work very hard, you have to work very smart, and let’s see where it takes us.”

Rodgers was not one to play defensively in Europe in his first spell as Celtic manager and predecessor Ange Postecoglou did not compromise any of his attacking principles last season as Celtic collected two points from a group campaign that promised more.

When asked whether he would adapt on European nights this season, the former Leicester manager said: “We are not at peak Celtic, I would say.

“We have got a long way to go before I think we will be where I am happy where I want us to be.

“However, what the players have shown is that flexibility.

“In terms of style, I don’t think there is a massive difference in terms of how the players have been asked to work. I just think it takes time and understanding for that to grow, and obviously of course it’s about players as well.

“You bring players back into the squad who are out of injured and of course the football can look different because you maybe have more dynamism and more flexibility and more movement.

“But stylistically at this level, we want to play the game to our DNA, which is be aggressive when we are attacking and have that conviction when we attack.

“And that all comes from when you defend. You have to have that collective responsibility and collective resilience and, if you have that in your defending, then you can look to show that in your attacking play.

“We know there’s times we are going to be under pressure, especially away from home, but of course we want to give Feyenoord a problem when we have the ball as well.”

Phillips saw his debut cut short on Saturday when he injured his ankle towards the end of the first half against Dundee.

The on-loan Liverpool defender was replaced by Lagerbielke at half-time, although he was only scheduled to play an hour in his first appearance since his move.

He trained at Celtic Park on Monday but Rodgers later said at the De Kuip Stadium in Rotterdam: “Nat has rolled his ankle so we will just have to see on that.”