Earlier on Friday, the Belgian television channel VRT reported that a group of journalists had learned which players had been left out of Belgium's final squad after visiting a warehouse in the Belgian town of Maldegem where they saw 23 personalized mattresses, labeled with the players' names and ready to be shipped to Russia for the team to use during the tournament.

"The story of the mattresses is not true. Nobody sent a list to anyone," Martinez was quoted as saying by the team's official Twitter account.

The head coach is set to announce the country's final squad by June 4.

Russia will host its first-ever FIFA World Cup from June 14 to July 15, with the games taking place at 12 stadiums in 11 cities across the country. Belgium will face Panama, Tunisia and England in Group G.