The Australian international was injured in a heavy studs-up challenge from Yordany Alvarez during the weekend's 4-3 win over Real Salt Lake and will now spend up to four weeks on the sidelines.
Cahill was felled in the fourth minute but managed to stay on and score the Red Bulls opening goal in the 11th minute before succumbing to the pain in the 85th minute of the seven-goal thriller prompting praise from head coach Mike Petke.
"It shows what kind of mentality he has what kind of warrior he is. I needed to make sure it was from the reckless challenge and not from (staying on). I was assured it was 100 percent an impact injury," said Petke. "It's a very big loss.
"It was a reckless and careless challenge. It was unintentional; I don't think Real Salt Lake plays like that. But it was a careless challenge to the knee and it's a big loss. We're looking at 3 to 4 weeks."