Countries will be able to name 26-man squads for this summer's Euro 2020, UEFA has confirmed.
Squads for the tournament will be able to include three more players than usual in case of positive tests for Covid-19 and subsequent spells of quarantine. However, matchday squads will only be allowed to contain 23 players.
UEFA also confirmed that coronavirus is classed as a "serious illness", meaning a player can be replaced if he tests positive before a team’s first match.
The governing body said in a statement: "To mitigate the risks of teams facing a shortage of available players for certain matches due to possible positive Covid-19 tests results and subsequent quarantine measures ordered by competent authorities, it has been decided to exceptionally increase the player list for all participating teams to 26 players.
"However, 23 players shall remain the maximum number permitted on the match sheet for each individual match (in accordance with Law 3 of the IFAB Laws of the Game permitting a maximum of 12 substitutes to be named for A-national team matches), including three goalkeepers.
"Once the player list has been submitted on 1 June 2021, the current regulations allow unlimited replacements on the player list in case of serious injury or illness before the first match, provided that the replacements are medically certified.
"For the sake of clarity, players who have tested positive for Covid-19 or who have been declared as 'close contacts’ of a positive Covid-19 tested person – and therefore put in isolation – by way of an authorities’ decision are considered cases of serious illness and can therefore be replaced before the first match with the approval of the UEFA administration."
UEFA said goalkeepers would be able to be called up in case of injury or illness before each match.
Dublin's Aviva Stadium had been due to host four games in the rescheduled tournament, which runs from 11 June to 11 July, but UEFA last week moved those fixtures to Saint Petersburg and London after the FAI and the Government were unable to guarantee that fans could attend. Games planned for Bilbao have relocated elsewhere in Spain, to Seville.