Thiam has been struggling with her Achilles tendon and missed recent Diamond League meetings in Monaco and London, and pulled out after two events at last weekend's Belgian Championships.
Belgian Athletics confirmed that Thiam's participation is uncertain while her coach Michael Van der Plaetsen told Le Soir newspaper: "It remains to be seen how her tendons will react to the upcoming intensive training sessions.
"Tendonitis never comes at the right time. If you don't slow down, things could get worse."
She is the defending champion in the heptathlon in Budapest, where the championships are being hosted from August 19th-27th. Last year in Eugene she won her second world title and also won in London in 2017.
In March, Thiam, who won Olympic gold at Rio in 2016 and Tokyo five years later, broke the pentathlon world record with 5,055 points at the European Indoor Athletics Championships in Istanbul in March.
