Big issues of the 2017-18 Bundesliga

Bayern Munich kick off the new Bundesliga season on Friday when Bayer Leverkusen visit the Allianz Arena, with Carlo Ancelotti's side chasing a record sixth title in a row.

They started the campaign by winning the DFL-Supercup but their poor pre-season showed signs of fallibility and will have given hope to Borussia Dortmund and RB Leipzig for the title race to come.

At Hoffenheim, Julian Nagelsmann's thriving coaching career will face the fresh complication of balancing European football with domestic challenges – something Leipzig must also cope with.

With sweeping rule changes introduced, including the use of VAR, and the promotion of their first female referee, there will be plenty of intrigue surrounding the start of Germany's top flight in 2017-18...

ARE BAYERN GOING BACKWARDS?

Bayern were pushed hard by surprise package Leipzig last season before eventually claiming a record fifth title in succession, but few would consider Ancelotti's first season in charge to be a resounding success.

They exited the Champions League at the quarter-final stage against Real Madrid, albeit amid some controversial refereeing decisions, and Dortmund got the better of them in the semi-finals of the DFB-Pokal.

There were signs that the team was beginning to take Ancelotti's desired shape as Corentin Tolisso and James Rodriguez arrived, but their pre-season was frankly miserable. They lost to AC Milan, Inter, Liverpool and Napoli without scoring, and even their 3-2 win over Chelsea was mitigated by the fact that they nearly let a three-goal lead slip.

The penalty shoot-out win over Dortmund in the Supercup was a welcome shot in the arm but doubts persist over this Bayern team. Douglas Costa's exit puts further pressure on the ageing frames of Arjen Robben and Franck Ribery, Jerome Boateng continues to struggle with injury and there seems to be no cure in sight for the peculiar affliction of Thomas Muller, who is so very far from his very best form.

Leverkusen were narrowly beaten at the Allianz Arena last November and they represent a difficult opening test for Ancelotti's side. He really needs a strong statement from his players if he is to keep the critics at bay for the time being.

BOSZ HAS A BIG POINT TO PROVE AT DORTMUND

Thomas Tuchel's time at Dortmund ended in fairly unsavoury fashion, with CEO Hans-Joachim Watzke hinting at a lack of respect on the part of the head coach as he left only three days after winning the DFB-Pokal.

BVB turned to Peter Bosz as his replacement after being impressed by the brand of football produced by his Ajax side, but the 53-year-old comes into the new season with plenty of doubts around his credentials.

Granted, Ajax were one of the tournament's most exciting teams as they reached last term's Europa League final, but they were swept aside in routine fashion by Manchester United. Bosz later complained of Jose Mourinho's long-ball tactics, prompting the Portuguese to respond with the eternally-quotable "Poets don't win titles".

He raised a valid point. Ajax were entertaining last term but ended up with nothing to show for it, Feyenoord beating them to the Eredivisie title and Cambuur knocking them out of the domestic cup. Dortmund prize thrilling football but the fans won't be content if the trophies do not follow.

LEIPZIG AND HOFFENHEIM: SHARED CONCERNS BUT VERY DIFFERENT SUPPORT

Last season saw refreshingly brilliant performances from Hoffenheim and Leipzig, although only one was greeted warmly by German football fans.

The antipathy towards Leipzig, fuelled by the organisation of the club and its funding by Red Bull, only grew as they mounted a shock title challenge and qualified for the Champions League in their first term in the top flight.

Hoffenheim won far more admirers as Nagelsmann, the youngest head coach in Bundesliga history, steered them to a fourth-place finish at the end of a season in which they didn't lose a league game until January 28 (against Leipzig, no less).

It will be difficult for these sides to balance European and domestic commitments in 2017-18, as neither boast squads to match the size of Dortmund or Bayern. But it's safe to say that a number of Bundesliga followers would be happy if only one of them managed to do so.

DO OR DIE FOR VAR

The Bundesliga prides itself on being at the forefront of the modern game and the announcement that video referee systems would be introduced for 2017-18 was greeted with general acclaim.

VAR is facing an uncertain future, though. A less-than-smooth trial at the Confederations Cup in Russia threw up more concerns about the process of referring incidents to video assistants; Germany boss Joachim Low described one such moment in their final win as "quite a mix-up".

The process in the Bundesliga will involve all 23 referees also serving as video assistants on matchdays and they will intervene on major incidents, including goals, red cards, penalty calls and cases of mistaken identity.

But with the decision to refer the incident still in the hands of the official on the pitch, it's hard to see the roll-out being an entirely successful one. And with clubs now allowed to show matches on big screens in the ground, parallel to the action on the pitch, it sounds like a thankless task for those in the VAR van.

STEINHAUS MAKES HISTORY AS GROUNDS ARE TOLD TO COVER UP

Bibiana Steinhaus will become the first female referee to officiate a Bundesliga match this season, with her promotion from 2.Bundesliga duties confirmed in May.

The 38-year-old is vastly experienced in German league football and officiated the women's gold medal match between Japan and the United States at the London Olympic games in 2012.

It's a commendable decision by the Bundesliga and the highlight of a host of changes to regulations in the division.

Along with VAR and big-screen footage being introduced, clubs will also be required to ensure that every seat in the stand is covered, guaranteeing that, as the Bundesliga put it, "only the players will be rained on at matches from now on".

Games are being more evenly split between Sunday and Monday to ease the burden on clubs in the Europa League, too, and even a change in the way numbers are entered into the electronic board prior to substitutions has been brought in, in order to allow the fourth official to stay focused on matters on the pitch.