The Daily Mail says the 22-year-old stopper joined up with his international team-mates on Thursday - three days later than the rest of the squad - after he was substituted following a clash with Alexis Sanchez on Sunday.
And after coming through a Thursday night training session unscathed he will start in Brussels, subject to further neurological tests on Friday.
Chelsea allowed their new No 1 to answer his country's call after he was passed medically fit, but reports in Belgium suggest they would prefer for him to be rested with Courtois still suffering from a minor headache.
Belgium manager Marc Wilmots told his Thursday press conference: "I do not understand the discussion on Courtois.
"If he is fit and wants to play, he will. If not, then it will be Mignolet. I will decide after training."
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