The uncapped Casteels was expected to be Belgium's third choice keeper at the Brazil finals, behind Thibaut Courtois and Simon Mignolet.
Casteels collided with Hertha Berlin's Colombian striker Adrian Ramos during the second half of their Bundesliga clash and has since undergone surgery.
"We support you during your recovery and hope to see you again soon," tweeted Belgium coach Marc Wilmots.
Casteels is the second player Belgium have now lost to injury, following Christian Benteke's ruptured Achilles tendon last week.
(Reporting By Philip Blenkinsop, editing by Robert-Jan Bartunek and Justin Palmer)
