Tests for ACL and Collateral ligaments can be performed at day-1.
Tests for PCL and Menisci can be done after 3 weeks of injury.
Next Steps
MRI can be done on day 1 of injury to detect ligamentous problems radiologically although that have to be confirmed clinically before proceeding for surgery.
Health Tips
Clinical tests can help with part and site of injury but not the grade or 'how much' the part is injured.
Arthroscopy is gold standard for diagnosis of ligamentous injuries.