The tournament, which starts in Qatar on 20 November, has been surrounded by controversy, BBC Sport reported.
Qatar has been criticised for its human rights record and its treatment of migrant workers.
Peaceful protests have been planned by some players.
England's Harry Kane and nine other captains of European teams will be wearing 'One Love' armbands.
Denmark will wear "toned-down" shirts for the World Cup to protest against Qatar – their kit provider Hummel said it "does not wish to be visible" in a tournament it claims "has cost thousands of lives".
Paris, and other French cities, are refusing to screen World Cup matches in public areas, despite France being the defending champions.
Speaking this week Liverpool manager Jurgen Klopp said it was "not fair" to expect players to make political statements or protests at the tournament.
Other off the field issues include Russia currently being banned by FIFA over the war in Ukraine. In addition the Ukrainian FA have called for Iran to be banned from the World Cup for alleged "systematic human rights violations".
The World Cup has been moved to the winter for the first time. Qatar initially proposed to host the finals during the summer in air-conditioned enclosed stadiums, but the plan was rejected.
Qatar's World Cup organisers state "everyone is welcome" to visit the country to watch the football, and that no-one will be discriminated against.
Now the game's world governing body has now written to all competing nations.
In addition to calling on countries to "now focus on the football" the letter, signed by FIFA president Gianni Infantino and secretary general Fatma Samoura says: "Everyone is welcome regardless of origin, background, religion, gender, sexual orientation, or nationality."
It also states: "We are aware that there are many challenges and difficulties of a political nature all around the world.
"But please do not allow football to be dragged into every ideological or political battle that exists."
Seven new stadiums have been built for the event, as well as an airport, roads and about 100 hotels. Qatar's government says 30,000 foreign labourers have been hired just to build the stadiums, with most coming from Bangladesh, India, Nepal and the Philippines.
Human rights groups have complained about the treatment of foreign labourers in Qatar, and the number who have died there.
In February 2021, the Guardian said 6,500 migrant workers from India, Pakistan, Nepal, Bangladesh and Sri Lanka had died in Qatar since it won its World Cup bid.
The number is based on figures provided by the countries' embassies in Qatar.
However, the Qatar government said the total was misleading, because not all the deaths recorded were of people working on World Cup-related projects.
The government said its accident records showed that between 2014 and 2020, there were 37 deaths among labourers at World Cup stadium construction sites, only three of which were "work-related".
BBC Arabic has also gathered evidence which suggests Qatar's government has under-reported deaths among foreign labourers.
England's Football Association has backed calls for compensation to be awarded for "any injury or death related to any construction project" for the World Cup.