The former Belgium international was dismissed from his job after the much-fancied side lost their Euro 2016 quarter-final against Wales and has since had a short spell in charge of the Ivory Coast.
But the manager and Chelsea goalkeeper Courtois feuded throughout the tournament, which included criticism of the manager’s tactics from the 25-year-old.
Speaking to BeIN Sports, Wilmots said: ‘I just have a problem when I make my selection at 6pm and at 6.15pm it is on all social networks.
‘It means that a player has sold the selection. And that’s serious. It came back to me from several French journalists that Courtois’ father was doing it. It means that you do not respect your homeland.
‘I find it a shame, because I have to wait an hour before the match to have the opposition’s selection. And that’s terrible.
‘The opponent is gaining time. He can prepare everything. He knows everything. And that’s really dramatic. It never happened at the World Cup in Brazil.’
Thierry Courtois hit back at Wilmots: ‘I never in my life communicated a team composition to any journalist.
‘Being a top player and also in a technical staff of a European level club, I know how delicate it is.
‘My team-mates and players also knew it. We work together for a long time to get results, I hate leaks.’