"The national team is spending a long time inactive," said Guimaraes.
"The players will arrive after playing an excess of matches in the domestic championship.
"Many are injured and the club sides don't play the same way as the national team.
He added: "What we're most worried about are injuries to key players a few days before the World Cup, when there won't be time for them to recover.
"The problem here is the large number of matches in the local championship, as it's not as easy for a tired player to recover from injury as one who's not tired."