First of all, do you have any fracture over your knee? Is your weakness is cause by pain?
Both of the above question will affect the rehabilitation direction.
In your case, if your weakness is not due to pain, you may need a lot of soft tissue release (by manual method) to soften injured soft tissue and let them to regain function.
Another factor is that you may also have the back injury during you hurt your knee with no back pain! Many people missed this component also. Thus you should find a physiotherapist to check it!