Public broadcaster VRT showed footage of mattresses being loaded up by a Belgian bedding company before their departure for Russia with labels indicating the player for which they were designated.
Belgium coach Roberto Martinez has named a provisional squad of 28, which will be whittled down to 23 on Monday after a friendly international against Portugal on Sunday (AEST).
However, based on the mattresses, the cut has already been made, given there were only 23 on show.
The indication is that goalkeeper Matz Sels, defenders Christian Kabasele and Jordan Lukaku, midfielder Leander Dendoncker and winger Adnan Januzaj will not be flying to Russia.
Their absence would not be a great surprise, although it would confirm the inclusion of some of the more fringe players in the squad, such as defender Dedryck Boyata or forward Christian Benteke.
Belgium will also play friendlies against Egypt and Costa Rica before opening their World Cup campaign against Panama on June 19. Their group also includes England and Tunisia.