Courtois joined Chelsea in 2011 from Genk, but has spent the past three seasons on loan at Atletico Madrid.
Wilmots believes that the 22-year-old will be playing at Stamford Bridge after the the conclusion of the World Cup and he expects the Blues to sell their current number one Petr Cech.
"Yes, he will be returning to Chelsea this summer," Wilmots told reporters. "Will they sell Cech? Yes, probably."
Courtois played for Belgium in their 1-0 win over Russia at the World Cup earlier today.