The Brazil international suffered the setback during the Ligue 1 champions' 1-1 draw with table-topping Monaco on Sunday and was forced off in the 16th minute.
The center back wrote on his official Instagram account that he would be out for around around six weeks on Tuesday, but Blanc refused to put a date on the influential defender's return though he accepted that his absence could have an impact on PSG.
"Thiago has undergone tests that have confirmed a problem with the muscle and the tendons," Blanc told reporters. "So it is not just muscular, and I think he will be out for a certain period. I am not a doctor, I can't be more precise.
"Obviously it’s a big blow in terms of timing. Whenever you lose a player it is a blow, and when it's a key player it is a very big blow.
"But we must deal with it. We have players available and we need everyone considering our [busy] schedule."
The 29-year-old ex-AC Milan star is set to miss key league games against Olympique de Marseille and Saint-Etienne, while Les Parisiens are unlikely to have him available for Champions League ties against Benfica and Anderlecht.
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