Crystal Palace boss Patrick Vieira says it is "not ideal" so many senior players are absent from his club's tour of Singapore and Australia.
Palace have said some players were not fit and others did not meet entry requirements for the countries "when travel arrangements were made".
Vieira said he would not discuss the players' Covid-19 vaccination status.
Travellers entering Singapore, where Palace played Liverpool on Friday, have to be fully vaccinated. Similar restrictions for Australia were lifted earlier this month.
"It is not the ideal situation for a manager to have so many players behind," said Vieira, before Tuesday's match with Manchester United at the Melbourne Cricket Ground.