England’s Nations League match against Iceland is in doubt because of the UK government’s new travel ban on non-UK visitors coming from Denmark.
Iceland are set to play Denmark in Copenhagen three days before facing England at Wembley on 18 November.
“Unlike other travel to the UK, there will be no exemptions to this quarantine policy,” the guidance says.
Since June, elite sportspeople have been exempt from coronavirus-related travel restrictions.
The Football Association is awaiting clarification from the government. The latest rules, which took effect at 04:00 GMT on Saturday, will be reviewed after a week, the Department For Transport said.
European football governing body Uefa’s coronavirus protocols state that international matches can be rescheduled at a date fixed by Uefa, or be played at a neutral venue if necessary.
BBC Sport has been told rescheduling is not an option. Uefa is understood to be studying the matter.
Denmark may drop England-based players
Under the new rules, UK citizens and visa holders can return from Denmark – but will have to isolate along with all members of their household for 14 days.
That means Denmark’s England-based stars would have to isolate upon their return if they travel to the country for international duty.
That would affect Leicester goalkeeper Kasper Schmeichel, Everton’s keeper Jonas Lossl, Chelsea defender Andreas Christensen, Southampton centre-back Jannik Vestergaard, Tottenham midfielder Pierre-Emile Hojbjerg, and the Brentford pair Henrik Dalsgaard and Mathias Jensen, who are all in the squad.
It could also affect the England-based players of Sweden, who are set to play Denmark in a friendly on Wednesday.
They include Manchester United defender Victor Lindelof, Newcastle full-back Emile Krafth and Everton goalkeeper Robin Olsen.
The Danish Football Association (DBU) says it has been in contact with Uefa, the Football Association and English authorities over the matter.
The DBU says as it has not “received the necessary answers from the FA”, the seven England-based players are “not expected” to play against Sweden.
They say as a precaution replacements have been called up in case “the English authorities do not have time to change the rules in the next few days”.
“We always have our strongest possible national team,” said head coach Kasper Hjulmand. “If the situation is not resolved, we look forward to seeing other, good players in action.”
Spurs manager Jose Mourinho has said Hojbjerg will not play in the friendly against Sweden, will miss the second game against Iceland as he is suspended, and will instead just travel to Belgium for the Nations League game on 18 November.
“It looks like we found a situation that protects us and the player and allows him to play one game,” said Mourinho.
World governing body Fifa’s rules, issued at the start of the pandemic, allow clubs to withdraw players from international duty if there is a risk of coronavirus infection.
Liverpool are also due to play away at Danish side FC Midtjylland on 9 December in the Champions League.