It's the issue which has divided the UK, dominating the news agenda and prompting debate from the high street to the Houses of Parliament. The result of Thursday's referendum on whether Britain should exit the European Union (Brexit) could change the way of life for many ... including those in sport.
It's not just politicians and grassroots campaigners who have been exercised by the possibility of Britain leaving the EU in recent days and weeks.
Top sports figures from the UK and elsewhere, including David Beckham, Arsenal manager Arsene Wenger, his club's defender Per Mertesacker and Ireland rugby international Tommy Bowe, have all had their say, urging the nation to stay.
Beckham took the unusual step on Tuesday of releasing a statement. It said: "We live in a vibrant and connected world where together as a people we are strong. For our children and their children, we should be facing the problems of the world together and not alone."
The Premier League's chief executive, Richard Scudamore, has even gone as far as to pledge the support of all his member clubs to the remain campaign, and if Britain votes to leave the EU the impact could be felt at both ends of the sporting spectrum.
The exact details of how Brexit would work may not become clear for some time if the referendum results in a decision to leave, but top domestic footballers as well and those involved with grassroots sport should be alert to potential change.
Leading British football agents have claimed that transfer fees for home grown stars like Harry Kane and Dele Alli could increase by as much as 40 percent if new regulations for European players were introduced.
There has been speculation, too, particularly surrounding the Premier League, that European footballers would need work permits, as those from outside the continent currently do, to play.
Football agent Sky Andrew said: "Whatever new regulations are brought in following a British EU exit, one thing for sure is that top British players would become more expensive.
"It could be as much as 40 percent because the football market is all about demand; that's what dictates transfer fees. There will be fewer European players for clubs to choose from as many may not meet the criteria to play in the Premier League.
"British players are already over-priced and this will only get worse because they will be in greater demand."
Barry Silkman, a high-profile British agent, claimed that the impending Brexit vote had already had an impact, causing the current transfer market to stagnate.
"You usually get some big deals being negotiated around this time, which are never made public," he said. "If Britain leaves the EU the cost of domestic players would increase and that's led to a lot of uncertainty among agents because nobody is quite sure at the moment on the final value of a player."
Silkman also claimed that any new regulations for European footballers would not adversely impact the Premier League in the long run because of its commercial success and political clout.
Dr Gregory Ioannidis, a sports law specialist at Sheffield Hallam University, concurred: "The EU already recognises the special nature of sport and will probably accept a more flexible approach to the movement of European players.
"It already has a number of specific agreements in place with non-EU states and I do not see why Britain would not be able to negotiate in similar fashion. Brexit will not necessarily be damaging for Premier League football."
Scudamore, however, insisted that the UK changing the European political status quo would make it a lot harder for the phenomenal commercial success of the competition -- which has worldwide television contracts worth £8.3 billion -- to continue.
"We would just be respected less around the world for not wanting to be part of something," Scudamore told the BBC. "Nobody bears the scars more than me of having to go and negotiate in Brussels [at the EU headquarters] and try and organise things a little bit in our interests in terms of the European machine.
"Ultimately you can't break away, you can't just pull out, you have to get in and negotiate and try and organise and try and influence."
At the grassroots of British sport, the idea of a future outside the EU has brought alarm.
The European authority has identified grassroots sport as a priority, citing the positive contribution it makes to society and the economy and contributing financially to ensure its wellbeing.
The bulk of EU funding for its jurisdiction has been channelled through a programme called Erasmus+, which was launched in 2014 and made €265 million over a seven-year period (2014-2020), split approximately among all 28 member nations.
The funds are not meant for specific sports or clubs looking to buy equipment but for those who use sport to tackle wider issues such as social inclusion, equal opportunities, good governance and improving health. The EU also launched a European Week of Sport last year to increase grassroots physical participation.
Leigh Thompson of the Sport and Recreation Alliance, which represents more than 300 British sports organisations, said: "In the event of Brexit, UK sports bodies would no longer be guaranteed access to these funds.
"Taking Erasmus+ Sport as an example, only full member states are able to participate in all funded projects."
Last year, British organisations received around €1.3m in Erasmus+ sports funding, a significant amount at the grassroots level. One of them was Dungannon United Youth, a football club based in Northern Ireland that uses the game to bring together Catholic and Protestant youngsters and those from other communities living in the area.
With 12 teams and a total of 300 players aged between 12 to 18, Dungannon received €15,000 to run some community programmes and take its under-14s team to a youth football tournament in Spain.
Club chairman Joe McAree said: "Without EU funds we would not be able to survive and if there was to be a Brexit then I pray that money would be made available to us through another body."
The club has been in the process of securing further EU funds to help with the construction of a new building that will contain a gym and classrooms so that it can offer educational programmes to its young footballers. The money has also been earmarked for hiring full-time teaching and football coaching staff.
McAree added: "The EU money has been a godsend for grass roots organisations like ours who struggle to raise funds. It allows us to do a lot of important work, which would not be possible if Britain was out of Europe."
Other organisations that have been funded by Erasmus+ include Street Games, which uses sport to work with disadvantaged communities, and the Special Olympics, which provides sport training and competitions for children and adults with intellectual learning disabilities.
Those campaigning for Britain to leave the EU have insisted that fears about the negative impact on sport amounted to scaremongering by those who want it to remain.
A spokesman for Leave.eu said: "The money that Britain saves by not being part of the EU could be used to fund all these grass roots sports programmes.
"As for professional football, players from outside of Europe currently don't have any issues if they meet the criteria for work permits and there's no evidence that there could be problems in the future if Britain leaves the EU."
Key questions ahead of Thursday's vote
What is happening?
On Thursday, voters will decide in a referendum whether or not Britain should leave the European Union, the economic and political organisation of 28 European countries.
How does the EU influence sport?
While EU laws greatly influence immigration and economics in member states, the organisation is less involved in sport. It plays a supporting role to national governments and helps coordinate events and initiatives with governing bodies.
Does sport benefit from a nation's EU membership?
Professional leagues across the continent certainly benefit from the EU's policy freedom of movement. Any EU citizen has the right to move and work in any member state, allowing top teams to recruit talent easily from across the continent.
How would a 'Brexit' affect football?
Premier League bosses have warned that the removal of the EU's freedom of movement would make it harder for them to sign top players. Players from EU member states are currently free to play in Britain, while those from non-EU states must meet strict visa requirements. Estimates suggest two-thirds of European players in Britain would not meet the requirements asked of non-EU players if there is a vote to leave.
What about other sports?
British rugby and cricket could be affected in a similar way if the country exits the EU. While most foreign players in these sports come from nations outside the EU, agreements mean such players also benefit from the EU's freedom of movement laws and are not technically treated as 'foreign'. Both rugby and cricket have strict rules for the number of foreigners allowed in squads and negotiations would be needed in order to stop those players becoming ineligible in the event of an exit.
What is going to happen?
The referendum result is not quite 'too close to call', but it has been a tense campaign. The 'Remain' camp has been ahead in the polls, but Leave enjoyed a surge in support a week before polling day. The website WhatUKThinks.org produces a poll tracker which suggests Remain leads by just two points on 51%. With politicians and voters split on the subject, a victory for either side is likely to be a narrow one.