The obvious good news is that it’s not an ACL tear. The obvious bad news is that it requires surgery.
How serious is a meniscus tear? A recent example of this injury is Blake Griffin, who tore his medial meniscus (Chase tore the lateral meniscus–I don’t know if that’s a meaningful difference) in July during Team U.S.A. workouts and was ready to go in Clippers training camp in October. A rough estimate for his timeline would be 2 or 3 months, I think. They’ll know more after surgery.