Danish football officials fear they will be unable to clear up their differences with the national team's senior players before Sunday's Nations League qualifier at home to Wales.
The Danish FA (DBU) and the squad have been in dispute for some time, image rights the main cause of complaint but relations between the two parties are at an all-time low.
John Jensen took charge of last night's friendly away to Slovakia, a game boycotted by the established players in the Danish squad as well as fringe players from the domestic league, with a squad made up mainly of futsal players appearing in Bratislava.
UEFA are keeping a watching brief on events ahead of Sunday's competitive game in Aarhus but there is a fear in UEFA circles that a repeat of last night, with Denmark playing amateurs in a 2-0 friendly defeat to Slovakia, would bring the new Nations League competition into disrepute.
"It wouldn't be fantastic for the competition if it did go ahead," Martin O'Neill said last night.
The players are sticking to their guns and maintain that their row with the DBU over image rights and other matters is not just about money but is about respect.
"We live in a professional football world where there must be orderly relationships. We must have our freedom to make our own personal agreements when we are not with the national team. And we will not be in breach of our club agreements by playing for the national team," said defender Simon Kjaer.
But the DBU are also standing firm. "There has been an offer, which I hope the players will think about carefully and thoroughly. If the players do not accept that offer, we'll have a serious situation again on Sunday, because the offer will not be different," said DBU President Jesper Moller.