Brendan Rodgers has sounded a tentative warning to the Celtic defence that they need to toughen up ahead of the season that lies in wait.

The Parkhead side have a headache regarding their central defence ahead of the UEFA Champions League qualifiers against either Flora Tallinn or Gibraltar Red Imps, a game due to be played on either the 12th or 13th July.

With Jozo Simunovic struggling after undergoing surgery on a knee injury in March and Dedryck Boyata also sidelined with a hamstring problem, there is an anxiety about available personnel with Danish defender Erik Sviatchenko, a committed stopper who made a decent impression following his arrival in the January window,and the Efe Ambrose the only fit and available central defender. Charlie Mulgrew is believed to be contemplating a three-year contract offer on reduced terms from the club.

Simunovic, whom Celtic paid over £5m for last August, featured in just 11 league games last season due to various injury issues and Rodgers as hinted that he will look for his defenders to toughen up as he looks for continuity over the course of the season.

“It’s an area where you need to be robust,” he said. “If players are going to play 50 or 60 games a season you normally find that your centre-halves will play those games.

“So at the minute we have a few of those injured and not fit. But it’s where it’s at and we need to look to see when we can get them back. If they are not going to be ready it’s a scenario we need to look at.”

Simunovic is unlikely to play in any of the qualifying rounds for the Champions League.

“It’s time,” said Rodgers. “In these early stages of pre-season he won’t be ready. That’s going to be into August from what I hear from the medical team.”

Meanwhile, as Celtic strive to make it into the group stages of the Champions League, former Hearts manager John McGlynn will be given a significant role in Rodgers’ backroom team.

McGlynn, who joined Celtic in a scouting capacity last January, will play a crucial role in the new structure at the club as Rodgers looks to involve him in the preparatory work that goes on before games.

The two men crossed paths when Liverpool and Hearts met in Europe in 2012 with McGlynn making an impression on the then Anfield manager.

“John has been a manager before,” said Rodgers. “I came across him when Liverpool played Hearts in the Europa League and was very impressed. He’s a good guy with good knowledge of the game.

“He’ll get to see over the coming weeks how I work, but he’s a coach and he knows football. He’s someone I’ll look at specifically to do that. He knows opponents; he knows Hearts well for a start!

“John is looking forward to that position and it will be great for him. He’ll have a handle on Scottish football. I always look to have a technical analyst who will watch opponents. I always look within the club to see who is there and the I bring my people in with me. We have that, along with John McGlynn.”

There are just under three months until the opening group games of the UEFA Champions League kick-off and Rodgers remit is to guide Celtic into that environemnt. It is a challenge that has been proved unsuccessful in the last two seasons and the Northern Irishman attributes the notoriously fraught qualifiers down to the timing of the games.

“Three or four months into the season, you are fit, strong and players are adapted to your way of working,” he said. With these, you are just two or three weeks into it and, suddenly, the qualifiers are upon you. That’s the way it is and it’s what makes them dangerous.

“They are tough games and some of the sides are well into their seasons, so they have played and have the level of fitness. But we are going to give everything we possibly can. It’s 12 weeks to the night when the group stages start and let’s hope we are in it."