Gylfi Sigurdsson

It’s hard to imagine where Swansea would be without Gylfi Sigurdsson.

The Icelandic international has been at the centre of everything the Swans have achieved over the past two-and-a-half years, both positionally and figuratively.

Sigurdsson has scored or assisted 38 of Swansea’s 100 Premier League goals since he joined the club for the second time in July 2014.

His influence was clear against Crystal Palace last weekend, when he scored a stunning free-kick, set up two goals and provided deliveries that led to two others in a 5-4 win.

Set pieces can be a vital source of goals for a side battling relegation, and in Sigurdsson, Swansea have one of the league’s best dead-ball specialists.

The 27-year-old has netted six direct free-kicks since his Premier League debut in 2012 – the joint-most of any player, along with Christian Eriksen and Juan Mata.

Jermain Defoe

With seven goals this season, Jermain Defoe is on par with some of the Premier League’s most prolific – and expensive – scorers.

Zlatan Ibrahimovic, Alexis Sanchez and Eden Hazard have scored as many as the Sunderland man, while Harry Kane, Roberto Firmino and Jamie Vardy are lagging behind.

No player in the Premier League has netted a higher percentage of his team’s goals this season.

For two years Defoe has been leading the line for one of the league’s weakest sides, playing in a lone-striker role that conventional wisdom would suggest a player of his size is unsuited to.

But few forwards can match the agility, intelligent movement and instinctive finishing, which combine to make Defoe one of the league’s most dangerous strikers, even at the age of 34.

Fraser Forster

Fraser Forster missed the first 20 Premier League games of last season, and Southampton struggled.

Having conceded 24 goals and won just six matches, the Saints sat 13^th in the table after a run of eight defeats in 10.

But then the giant Englishman returned, sparking a run of six consecutive clean sheets and helping the club secure a place in the Europa League.

Southampton have had one of the strongest defences in the Premier League for the past few seasons, but they are a vastly superior side with Forster in goal.

Their winning percentage surged from 36 to 67 after his comeback last season.

So while Virgil van Dijk and Jose Fonte are being linked with big-money moves away from St Mary’s, it is worth remembering the impact made by the man behind them.

Santi Cazorla

In the deeper midfield role that he has adopted in recent seasons, Santi Cazorla rarely scores or assists.

He is no less important to Arsenal, however, than when he occupied a more attacking position.

The 31-year-old has completed more passes per game than any of his team-mates this season, and his ability to drive forward is integral to the Gunners’ style of play.

Cazorla’s knee injury last November derailed the club’s title hopes, and their winning percentage dropped from 57 to 48 when he was absent.

The Gunners have endured similar problems this season. They won eight of the 10 games in which he appeared before damaging his Achilles in October, and have won just four of nine since.

So while Arsenal have perhaps the strongest midfield depth of any Premier League side, the season so far has proven that they are still reliant on the underrated Spaniard.

Toby Alderweireld

Tottenham’s results since Toby Alderweireld was injured in October are sufficient evidence of his value to the club.

Spurs have won just one of their nine games in all competitions, slipped to fifth in the Premier League, and crashed out of the Champions League with the Belgian sidelined.

Their defence, which had only let in four goals before Alderweireld’s injury, has conceded in each of Tottenham’s last six fixtures.

And while Kevin Wimmer and Eric Dier have previously appeared to be competent defenders alongside the former Southampton centre-back, they have both struggled badly in his absence.

It is no coincidence that last season, when Alderweireld played every game in the Premier League, Spurs went so close to winning the title.