Each of the 32 participating countries must send a list of a minimum of 35 players up to a maximum of 55 by the end of the day, in the first step in the selection process.
Coaches then have until November 14th to decide on their final list of 26 players by an 1800GMT deadline. FIFA will publish all the squads the next day.
The final squad must come from the preliminary list, with no allowance for any late changes of mind over the next three weeks, FIFA’s tournament rules and regulations stipulate.
World football’s governing body will not publish the preliminary lists but some countries might choose to do so, signalling their intentions and potentially putting to bed some of the early debate about team selection.
World Cup holders France have a long list of injuries that coach Didier Deschamps must take into consideration over the next few days although the preliminary list is long enough to include players in a race against time to be fit for Qatar.
England’s debate about their right back position might also get clarity as manager Gareth Southgate makes his choices. There has been speculation about whether Liverpool’s Trent Alexander-Arnold is in his plans after recently being overlooked.
Brazil left out Gabriel Jesus for two friendlies in France last month amid stiff competition for places in the forward line and despite his fine form for his new club Arsenal this season.
The number of players in the final World Cup squads have been increased by three - from 23 to 26 - for the tournament in Qatar.
FIFA said in June the decision to expand squads was made "given the need to retain additional flexibility due to the unique timing" of this year's competition, which will interrupt the European club season.
It kicks off on November 20th with the final on December 18th.
World football’s governing body also took into account the "broader context of the disruptive effects caused by the Covid-19 pandemic on squads before and during tournaments".
The number of players on the preliminary list was also increased to 55 from a maximum of 35 four years ago.
