Wilmots, who last week made known Januzaj's decision to play for Belgium, said he had not given any guarantees to the 19-year-old that he would be in the final squad in Brazil.
Wilmots told Belgian newspaper De Morgen that Januzaj had shown he could also play as a centre forward, a useful option given the unavailability of Christian Benteke due to injury.
The coach said he would select Januzaj in an initial squad of 26 or 27 for training camps, including friendlies against Luxembourg in Belgium on May 26 and Sweden in Stockholm on June 1.
"I first want to see how he is in training. I'll pick 26 or 27 players and say there's only one thing that counts - the pitch. Come on guys, show me what you can do," Wilmots said.
"That I'll take him on the camp is certain. I think that's normal given his performances in the last year."
Each football association must submit a list of up to 30 players of potential squad members by May 13, with the final 23 names sent to FIFA by June 2.
Born in Belgium to ethnic Albanian parents from Kosovo, Januzaj was eligible to play for a number of countries including Belgium, England, Albania, Kosovo, Serbia and Turkey.
He scored two fine goals in his first Premier League start at Sunderland and has shown great potential in an otherwise poor season for Manchester United.
Belgium, playing in their first World Cup in 12 years, will face Algeria, Russia and South Korea in the group phase in Brazil.
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