They say familiarity breeds contempt. For Christopher Jullien, though, it has been the key to Celtic's winning momentum and his successful first season at the club.

The Frenchman's relationship with central defensive partner Kris Ajer was a vital component in their Premiership winning campaign last year. And it helped Jullien settle in to a rhythm with a solid player beside him. A player who has been linked with a move out of Parkhead, as AC Milan continue to monitor his progress.

Jullien hopes his mate sticks around as he and the rest of the Celtic squad aim for their tenth title in a row as the pair continue to develop and improve together. They both know each other's game and have found the best way of working to nullify the attacking threat of any opposition striker. Albeit, Jullien admits, by the same token opponents have learned how to cope with the duo.

"Since I arrived my relationship with Kris has always been good and we try to keep that at the same level every day," Jullien said. "We do our best to improve every day, to be better every day. I think the season is going to be more different because now I know everyone, on the field and in the staff. I know the league and I know my opponents, but they know me too. So it will be harder. Sometimes when you know everything you can cheat a little bit so I don’t want to get in that mood. I want to double and treble my focus so I can do better than last year.

"Do I want Kris to stay? Yeah, definitely. When you play in a team you always want the best player with you and Kris is part of the team. He has been here a long time and is a big, big player for us. I'm here and I wish all players could stay with me but some will have good quality, like Kris. He will have some unbelievable clubs on his back for sure for years and years. But now I just hope that he will stay with me for the longest that he can."

Another player Jullien will have to get to know quite quickly is new signing Vasilis Barkas. A defence is only as good as its goalkeeper, after all. Barkas signed from AEK Athens last week and has been pitched straight into training with the rest of the Celtic squad. And his new teammate expects big things from the stopper.

Fraser Forster was a standout for Neil Lennon's charges last season and Jullien was a big fan of the Southampton loanee. Though he made sure to avoid any comparisons between the two goalies. "I don’t think it’s good to compare him with Fraser," he said. "The club and Glasgow knows what Fraser did for the club and last year.

"He is the best goalkeeper I’ve had at my back but comparing the new goalkeeper with Fraser is a mistake. He has his qualities and so does Fraser. We saw [Barkas] this morning. It was nice to talk to him a little bit. He’s just arrived so I have to think I’ll have to do a bit what the guys did last year to make him feel comfortable on the field.

"He’s a big guy and I think he’s played a lot of games to know what is needed from him. He knows the expectation of the club and I can’t wait to play with him. As a goalkeeper you need to be comfortable and he will probably have more advice to give to me. I can’t wait to play with him and see how he gets on in the team."

If Jullien is familiar with Ajer and hopes to become as such with Barkas, a completely unfamiliar aspect of the upcoming season will be the lack of supporters within stadiums. Fans - until September at the earliest - will not be permitted to watch games inside grounds across the country. And the defender, 27, admits it will be an unusual way feeling.

However, he expects himself and his teammates to overcome any issues and handle the behind closed door games without much hassle. "We are ready for that," he added. "It is not a situation that is normal. The Covid situation is not normal at all but we have to get through it and just stay focused on the goal that we have and it is to play game by game and winning points.

"We know that the fans are always behind us, even if they are watching on screen, and we just have to stay focused and get the job done on the field. I just cannot wait [for fans' return]. It is a difficult time right now but we know that they are behind us and it is going to be a great moment when they return."