The current Super League structure ensures that four Super League sides are in danger of being relegated from the top flight each year. In 2016, Hull KR were the Middle 8s Qualifiers' first victim, and in 2017 it was the Leigh Centurions who succumbed to the new system after just one year in Super League. Not one top flight side wants to be in the bottom four and thus to be at risk of relegation to the Championship, but, if the season does not go as planned, even teams which should be competing for silverware can fall into the Qualifiers' trap as Leeds Rhinos and Warrington Wolves found out in 2016 and 2017 respectively. Here are those sides that need to be wary going into the 2018 season.

Hull KR

Shock horror! The promoted side is first on the list, but this is just common sense. A newly-promoted side are always going to be in danger of going straight back down the following season - as Leigh found out in 2017 - as the top flight pace and skill is a step above that in the Championship. And, whilst some Championship fixtures may be a walk in the park - nearly offering so much as a bye for those at the top - the same cannot be said of any fixture in Super League. The Robins will also have to do it without outgoing half-backs Jamie Ellis and Jordan Abdull - both of whom were key men in KR's promotion-chasing year.

Hull KR do have one thing weighted heavily in their favour however. They have had just one year in the Championship after dominating the league in 2017 and, having been in the Super League since 2007, the Robins know what it takes to survive.

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And Rovers didn't even need the Million-Pound Game to secure top flight status once more in 2017, finishing third in the Qualifiers' table to earn automatic promotion. Though a relegation candidate, the Robins have recruited well, bringing eight-time Grand Final winner Danny McGuire to the club as well as Super League experience in the shape of Jordan Walne, Tommy Lee and powerhouse Mose Masoe. Thus, KR could well upset a few sides in 2018.

Widnes Vikings

After finishing bottom of Super League before the Super 8s split, many pundits and supporters predicted Widnes' relegation from the top flight. Yet, Denis Betts' side withstood a seemingly relentless injury list to end their tumultuous year on a very positive note, finishing second in the Qualifiers and thus automatically earning their Super League place for 2018. But, are they able to perform another miracle in 2018?

The Vikings have not exactly had the best of pre-seasons so far as head coach Denis Betts has been with the England national side throughout the recent World Cup.

Therefore Betts needs to work quickly if he is to ensure the Vikings avoid another disappointing season.

Recruitment has been both positive and negative for Widnes; whilst new signings Krisnan Inu and impressive PNG duo Kato Ottio and Wellington Albert promise to excite the Widnes faithful, the loss of Chris Bridge, Corey Thompson, Eamon O'Carroll, Jack Buchanan, Manase Manuokafoa and the disgraced Rangi Chase perhaps could prove decisive. The loss of experience and flair may hit the Vikings hard. But, if the likes of Joe Mellor, Rhys Hanbury and Lloyd White can stay fit, and, if the youth players that came into the first team because of injuries in 2017 - such as Danny Walker, Ryan Ince and Ed Chamberlain - perform as well as they did when given the opportunity, Widnes may defy expectations.

Catalans Dragons

There is no doubt about it that Catalans should have been in the top eight in 2017 with the squad that they possessed. After a sixth-placed finish in 2016, chairman Bernard Guasch would have been expecting to penetrate the top four in 2017. And, with an abundance of talent in their ranks in the shape of experienced and dynamic half-backs Richie Myler and Luke Walsh and intelligent hooker Paul Aiton amongst an array of French talent including Tony Gigot, Vincent Duport, Julian Bousquet and Jason Baitieri to name but a few, the top four is perhaps where they should have been.

But, after a very poor start to the season, including five losses in a row, Guasch cut ties with head coach Laurent Frayssinous - in charge since the end of 2012 - at the end of May. With Michael Monaghan as interim coach, things didn't improve and it took until mid-June before Steve McNamara was appointed as head coach. McNamara failed to arrest the Dragons' slide too, and the French side ended the season in tenth with just seven wins. Though they faced the Qualifiers, most expected them to breeze through as Warrington did; Catalans, however, finished a dismal fifth and had to endure the tortuous Million-Pound Game away at Leigh. Eventually winning 26-10, the Dragons secured their Super League status at the last moment.

With this experience behind them, Catalans may well be better equipped to deal with the same scenario if it occurs in 2018. Yet, will they really improve under McNamara? He had 11 games towards the back of end of 2017 to change things, but the Dragons barely improved. And, with the likes of Krisnan Inu, Justin Horo and Richie Myler all departing and stalwart Thomas Bosc retiring, Catalans have lost strike and firepower. New signings David Mead and Samisoni Langi have the potential to be devastating for the French side, but they have still not recruited enough quality to ensure there is no repeat of 2017. Catalans will either finally reach their potential in 2018 or will crash and burn as they did in 2017.

Huddersfield Giants

Though Huddersfield actually finished inside the top eight in 2017, they did so in rather unconvincing fashion. Just one point separated the Giants from ninth-placed Warrington. And, most of their nine victories came at a time when influential full-back Jake Mamo was firing on all cylinders. With 12 tries in nine appearances, Mamo was essential in the Giants' mid-season run of form, and, it was unsurprising that when he was once more sidelined from June until the end of the season, Huddersfield seemingly struggled. Since 2014, Mamo has played just 38 games and, though important as he is, his susceptibility to injury means he cannot be a player that the West Yorkshire side relies on, otherwise the Giants could find themselves in trouble.

For the past two years Huddersfield have flirted with relegation; in 2016, they faced the Qualifiers after finishing bottom of Super League and though they improved greatly in 2017, they were still far from convincing. And, though new recruits Jordan Rankin and Jordan Turner added something extra towards the back of end of the season, the Giants' squad for 2018 is extremely thin. The first-choice 17 boasts an incredible amount of talent, but past that, Huddersfield are largely relying on youngsters to fill the shirts. Yes, it will give these young players good experience, but, if the going gets tough, who will lead the team through?

Salford Red Devils

After scraping through the Million-Pound Game in 2016 by the skin of their teeth, Salford had a much improved 2017, eventually finishing seventh - though they were fourth before the Super 8s split. But, with outspoken chairman Marwan Koukash in the process of standing aside to be replaced by a clubs' trust, off-the-field, the Red Devils are far from stable. Ian Watson has done a fantastic job on-the-field, but, he is not a magician and the large squad turnover for 2018 could disrupt the side.

Eight have joined the club for 2018 whilst 11 have left and, although new recruit and Fijian international Ben Nakubuwai looks a real gem, the Red Devils have replaced the outgoing Michael Dobson and Todd Carney with the inexperienced Jack Littlejohn - whom has played just 21 times in the NRL since 2014. And, Warrington-bound Ben Murdoch-Masila leaves a huge gap, almost impossible to fill. Salford's shirt numbers go as high as 37, with many of those outside of the first team having little Super League experience. It could be a worrying time for Salford fans if the side starts to pick up injuries in 2018. #RugbyLeague #RL #SuperLeague