Wembley could be stripped of its host status for the Euro 2020 semis and final, if the UK Government fail to allow quarantine exemptions for travelling fans and officials.
London is one of 11 host cities for the tournament and is set to host England's clash with Scotland on Friday, having already housed their 1-0 victory over Croatia on Monday.
Wembley is set to play a bigger role as the tournament goes on: in addition to its three group stage games, it is in line to host two round of 16 matches, both semi-finals and the final on 11 July.
UEFA, however, are believed to be concerned about its viability as a host venue for the late stages of the tournament. As reported by various outlets, including The Times and ESPN, the UK's ten-day quarantine rule for overseas visitors has caused the governing body to consider its options.
As things stand, nine of the 11 host cities have agreed on an exemption to quarantine rules for those travelling from overseas to attend the game. That includes fans with a ticket, broadcasters, sponsors, officials and anyone with access to the venue.
In London and Glasgow, however, things are a little more complex. Only team staff have been granted an outright exemption; everyone else is subject to a quarantine period depending on where they are travelling from. With most countries on the amber list, that likely means ten days in isolation upon arriving in the UK.
UEFA fear that could dissuade fans from travelling to England for the games, and with Wembley set to be at 50% capacity for the knockout games, they want to encourage as many people to attend as possible. They have asked the UK Government to consider loosening their exemption rules, and if they fail to, the semis and final could be held elsewhere.
Hungary's Puskas Arena - which served as a late substitute for various Europa League and Champions League ties, and will have hosted four Euro 2020 games by the time the semis come around - is considered a viable plan B.