The Belgian international, 20, has not travelled with Leonardo Jardim’s squad for Wednesday’s match at Nantes and could be out until after the winter break.
“Youri Tielemans has a meniscus injury in the right knee following an injury in the last match. An arthroscopy is planned for the coming days,” the principality club said on Tuesday.
Tielemans joined the French champions from Anderlecht in the close season for a reported 25 million euros ($29.7 million).
Monaco’s hopes of defending the Ligue 1 title took a severe hit at the weekend as they slipped nine points adrift of leaders PSG, while they were also knocked out of Europe with a 4-1 Champions League defeat by RB Leipzig last week.
Italian defender Andrea Raggi will also miss the Nantes trip with a thigh problem.
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