Player contracts are no longer necessarily displays of loyalty, but what purpose they do serve is effective as protection for clubs in the transfer market, an insurance policy against players being poached for less than they might be worth.
Clubs can become vulnerable to losing players when contracts are expiring, facing either cut-price sales or watching them walk away as free agents thanks to the 1995 Bosman ruling. On the other side of the same coin, an expired contract will finally allow a club to release a player they might have been trying to move on for some time.
Should a club be unwilling to release a player on an expiring contract at the end of the season, yet remain unable to successfully negotiate a new deal, the only alternative is to find a buyer during the January transfer window so they can at least command a transfer fee.
Arsenal let Alexis Sanchez join Manchester United in January last season, able to arrange a deal that saw Henrikh Mkhitaryan head in the opposite direction. But the Gunners gambled on Mesut Ozil, refusing to sell in January in the hope they could tie him down to fresh terms before it was too late. They were successful on that occasion, but it was a huge risk.
Had no new contract been agreed, Arsenal would have been looking at a player potentially worth a minimum of £40m walking away for absolutely nothing. That, quite frankly is a football club's worst nightmare and one that everyone wants to avoid.
This is a rundown of every player from the Premier League's 'Big 6' clubs - Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham - who is currently on course to be out of contract at the end of the 2018/19 season.
Contract length data sourced from Transfermarkt
Arsenal
Aaron Ramsey will be a big loss for Arsenal in the summer after he recently effectively confirmed that this season will be his last with the club after contract talks broke down.
The arrival of new goalkeeper Bernd Leno in July could see Petr Cech let go without too much bother come June as the veteran stopper has made high profile mistakes this season.
It will, however, be interesting to see whether inconsistent forward Danny Welbeck is offered a new deal. Meanwhile, 32-year-old Nacho Monreal's versatility and experience will surely see the Gunners ask the Spaniard to stick around beyond this season.
Chances are that veteran summer signing Stephan Lichtsteiner might only last one season after only serving as a backup option since joining from Juventus.
Petr Cech (GK)
Nacho Monreal (DF)
Stephan Lichtsteiner (DF)
Aaron Ramsey (MF)
Danny Welbeck (FW)
Chelsea
Cesc Fabregas is no longer one of the first names on Chelsea's team sheet, although fans might argue that he remains better than other midfield options Ross Barkley, Danny Drinkwater or Tiemoue Bakayoko, who is currently out on loan at AC Milan.
No new contract would see club captain Gary Cahill, who will celebrate his 33rd birthday this coming December, released at the end of the season after six years and six major trophies in Chelsea colours.
David Luiz is actually back in the team this season after spending much of last season on the sidelines and speculation last month suggested Chelsea are ready to offer him a new contract as he remains of great value to the club.
Willy Caballero (GK)
Robert Green (GK)
David Luiz (DF)
Gary Cahill (DF)
Mateo Kovacic (MF) loan
Cesc Fabregas (MF)
Lucas Piazon (MF)
Olivier Giroud (FW)
Liverpool
Liverpool fans won't want to wave goodbye to dependable vice-captain James Milner on a free transfer and will hope the soon-to-be 33-year-old signs an extension before long.
Daniel Sturridge may view his expiring contract as a chance to consider his future and search for starting opportunities elsewhere after becoming little more than a backup option to premier front three Roberto Firmino, Sadio Mane and Mohamed Salah.
It has been rumoured that Spanish left-back Alberto Moreno has 'no intention' of signing a new contract, despite an offer being made, and is a free agent target for Arsenal, Real Madrid and Barcelona. The 26-year-old has barely played this season.
Flop Lazar Markovic hasn't played for the Reds' first team at all since May 2015. The Serbian has been loaned to Sporting CP, Hull and Anderlecht during that time.
Alberto Moreno (DF)
James Milner (MF)
Lazar Markovic (MF)
Daniel Sturridge (FW)
Manchester City
Manchester City fans won't lose much sleep about flop centre-back Eliaquim Mangala leaving the club as a free agent in eight months' time. He is currently back at City after an injury cut short a loan to Everton last season, but with John Stones, Aymeric Laporte, Nicolas Otamendi ahead in the pecking order there is no future for the Frenchman in Manchester.
Captain Vincent Kompany is a different story. The 32-year-old Belgian is City's longest serving player and recently hinted to the Daily Mail that he is keen to renew: "First of all, the situation with City is very simple. I am in a club where I feel so comfortable. I have an extremely good relationship with every single member of the club so there is absolutely no need for me to constantly go on about a contract situation."
Vincent Kompany (DF)
Eliaquim Mangala (DF)
Brahim Diaz (MF)
Manchester United
Prior to Luke Shaw's confirmed new five-year deal earlier this week, Manchester United could have fielded an entire XI of players whose contract is up at the end of the season.
Anthony Martial is one talent that fans will be desperate to see stay at Old Trafford, while loyal duo Juan Mata and Ander Herrera are other popular individuals with fans who would be sorely missed if they are sold in January or released in summer.
As far as goalkeeper star David de Gea is concerned, the club does at least retain an option to extend his contract by 12 more months to 2019 before the situation becomes critical.
David de Gea* (GK)
Antonio Valencia* (DF)
Chris Smalling* (DF)
Phil Jones* (DF)
Matteo Darmian* (DF)
Ashley Young (DF/MF)
Juan Mata (MF)
Ander Herrera (MF)
Andreas Pereira* (MF)
Anthony Martial* (FW)
James Wilson* (ST)
Note: Players marked with a star (*) have an optional year on their contract that can be triggered by United.
Tottenham Hotspur
Toby Alderweireld's contract situation remains an interesting one. The Belgian defender was heavily linked with Manchester United ahead of this season and many saw it as Tottenham's last chance to command a handsome fee for the highly rated 29-year-old.
It has been well established that Alderweireld has a clause in his contract that will allow Spurs to extend his contract to 2019, but also invokes a €25m release clause.
Centre-back partner Jan Vertonghen told the Belgian media of own situation in September, "My contract is expiring at the end of the season, but Tottenham have an option to extend it with one year. I think they will take up the option. We'll see what happens."
International colleague Mousa Dembele has been tipped to move to China when his is up.
Michel Vorm (GK)
Toby Alderweireld* (DF)
Jan Vertonghen (DF)
Mousa Dembele (MF)
Fernando Llorente (FW)