Milambo, a 20-year-old midfielder, jumped over a tackle and collapsed, grabbing his knee in pain. He was heard screaming in agony, which suggests a possible knee ligament injury.
Milambo was stretchered off just before halftime and replaced by FC Groningen midfielder Jorg Schreuders.
This was not the only injury suffered by the Netherlands team during the match. Como winger Jayden Addai was forced to leave the game due to a hamstring injury in the 20th minute and was replaced by AZ talent Ro-Zangelo Daal.
Milambo joined Brentford in the summer, moving from Feyenoord where he spent 11 years. He was reportedly signed for €20 million as a youth academy product.
Milambo started in the early stages of Brentford's season but was soon relegated to the bench, playing just 68 minutes across all competitions since September.