It's not clear what is the natural history of mild posterior cruciate ligament tears. Natural history refers to what happens over time after an injury occurs if no treatment is provided.
In the case of mild PCL injuries (grade one or two), it appears that the knee can recover. Rehab to help strengthen the muscles around the knee can help.
No one is quite sure what is the final outcome. Follow-up studies of athletes with PCL injuries are limited. There are some reports of permanent instability of the knee joint. Arthritis may develop resulting in a loss of knee function.
Until more is known, most experts recommend a rehab program to recover strength, proprioception (sense of joint motion), and endurance. A physical therapist can help set you up with such a program. Besides restoring more normal function, rehab may help prevent further injury and keep you in the game.