Liverpool’s problems mounted as Manchester United condemned them to a fourth consecutive defeat for the first time since 2014. They are not the only Premier League club in crisis right now.

Nottingham Forest have gone from a Champions League fight to a relegation battle, with Sean Dyche set to become their third head coach in a turbulent season following Ange Postecoglou’s sacking.

Wolves are winless after eight games at the bottom of the table and there are issues at West Ham too, with fans staging protests as Nuno Espirito Santo fights to turn their season around.

This week in Between the Lines, the new Sky Sports strand unpicking the data behind the biggest stories in football, we pull out the key issues behind each club’s struggles this season.

Liverpool: Salah, Wirtz woe and defensive dip

When does a loss of form become a decline? Mohamed Salah’s struggles put him near the top of Liverpool’s list of problems.

Salah produced one of the great individual Premier League campaigns last term, directly contributing to a whopping 55 per cent of Liverpool’s goals by scoring 29 times and registering 18 assists.

The drop-off has been stark. Salah has gone seven consecutive Premier League games without scoring a non-penalty goal for the first time in his Liverpool career. Jamie Carragher says that, at 33, he should no longer be considered a guaranteed starter.

His numbers show an alarming decline relative to previous seasons and, although he did spurn two good chances at Anfield on Sunday, his lack of goals is not just down to poor finishing.

More worrying is that his expected goals are trending the same way as his actual goals. Salah’s shots have dropped off and the underlying data shows he is not getting anything like as many high-quality chances as in previous seasons.

That despite the £116m addition of Florian Wirtz, who was brought in to bring creativity, as well as a goal threat, from midfield.

Interestingly, the 22-year-old has created chances at a higher rate than he did at Bayer Leverkusen. He is getting more touches in the opposition box too. But he is yet to register a goal or assist and is less involved generally than he was at his previous club. His overall touches, passes and take-ons are all down on last season.

Wirtz needs to build chemistry with his new team-mates and Alexander Isak and Hugo Ekitike find themselves in the same position. The tragic loss of Diogo Jota was, of course, completely unforeseen but are Liverpool suffering from changing too much?

There has been instability in defence too. Trent Alexander-Arnold’s creativity is a big miss, particularly for Salah, with whom he had an excellent understanding on Liverpool’s right flank, but his exit has also caused defensive upheaval. Conor Bradley and Jeremie Frimpong have struggled. As has Milos Kerkez, who has been preferred to Andrew Robertson at left-back.

With the previously dependable Ibrahima Konate and Virgil van Dijk taking it in turns to have poor games at centre-back, Liverpool have come to look vulnerable, conceding two or more goals in eight games out of 12 in the Premier League since the start of May.

“Liverpool are just not at the races at all defensively,” said Carragher on Sky Sports. “Until they fix that, they can’t win the league.”

Forest: Three styles in five weeks?

Nottingham Forest have gone from fighting for a Champions League spot to battling against relegation. A turbulent season has already claimed two head coaches, with Ange Postecoglou sacked after just 39 days and Sean Dyche now arriving to steady the ship.

Evangelos Marinakis has transformed the club’s fortunes since his takeover but the chaos of the last few months has undoubtedly had an impact on the pitch, with Forest in the relegation zone and their players trying to adapt to dizzying changes of style.

Forest’s success under Nuno Espirito Santo was built on a distinct tactical approach emphasising direct attacks over possession but Marinakis opted for the total opposite with Postecoglou.

The former Spurs boss attempted to overhaul their style, eschewing directness for short passing, build-up attacks and a far greater emphasis on possession. But his players struggled to adjust, with Forest failing to win any of his eight games in charge.

Dyche’s appointment signals another reversal. The former Everton head coach’s approach is much more in line with Nuno’s, although there are still significant differences. Dyche’s teams typically play higher up the pitch, proactively aiming to force high turnovers through pressing, whereas Nuno’s teams are more passive.

Postecoglou’s efforts to turn Forest into a pressing team were unsuccessful, leaving them defensively open all too often.

Dyche will need to get his messages across more quickly to ease the sense of crisis, especially with games against Porto, Bournemouth and Manchester United to come in the next 10 days.

Wolves: Cunha missed as signings struggle

Forest have at least won a Premier League game this season despite their struggles. For Wolves, the wait continues after a 2-0 reverse against Sunderland which kept them bottom, on only two points from eight games, with fans fearing the worst.

Their struggles are not particularly surprising. The Sky Sports supercomputer predicted Wolves would be relegated in 18th place at the start of the campaign following a summer of high-profile sales including those of Matheus Cunha and Rayan Ait-Nouri.

Cunha and Ait-Nouri are not the only previously important players to have left Molineux in the last two years. Nelson Semedo, Pablo Sarabia, Pedro Neto and Mario Lemina have also gone.

In total, 108 of Wolves’ 178 goals and assists across the last two full seasons in the Premier League were scored by players no longer at the club now, a share of over 60 per cent.

The latest round of sales benefitted the club financially, allowing them to make a net profit of £20.9m in the summer transfer window. But the players brought in as replacements are struggling to deliver.

Fer Lopez, Tolu Arokodare and Jhon Arias have only contributed one assist between them so far in the Premier League. Jorgen Strand Larsen, wanted by Newcastle during the summer, has also drawn a blank after making his loan move from Celta Vigo permanent.

The result is that Wolves have only found the net five times in eight games so far, leaving them at risk of getting cut off at the bottom of the table despite head coach Vitor Pereira signing a new three-year contract last month.

West Ham: Fans see underachievement

While Wolves have pinned their hopes on the coach who took them into the new season, West Ham have made a change, with Nuno replacing the axed Graham Potter last month.

The club hope the former Forest boss will change their fortunes following a poor start to the season but fans are staging protests over broader, long-standing issues.

The move to the London Stadium has increased the club’s revenue but the move remains a source of discontent for many fans.

The West Ham hierarchy have invested heavily since the stadium move in 2016, recording the sixth-highest net spend among Premier League clubs, ahead of even Newcastle and Liverpool.

But, although their Conference League success brought silverware, West Ham continue to underperform domestically relative to their expenditure, with questionable recruitment decisions contributing to a run of only three top-half Premier League finishes in nine seasons at the London Stadium.

For now, Nuno will continue his efforts to turn their season around. But clearly there is work to do in the long term to rebuild relations between fans and the club’s ownership.

Read last week’s Between the Lines

Where are all the English No 9s? Last week we took a look at the national team’s reliance on Harry Kane and the worrying decline in goals scored and minutes played by English strikers.

In a bonus Between the Lines, we also looked at Cristiano Ronaldo’s remarkable scoring rate and assessed his chances of becoming the first player in history to reach 1,000 recorded goals.