Loss of muscle bulk (atrophy) isn't uncommon after a knee injury or knee surgery. Muscle atrophy and a loss of muscle strength are natural consequences of using the leg less after surgery.
A recent study of 29 PCL repairs showed about half the patients recovered 90 percent of their normal muscle strength. This was measured for the quadriceps muscles (knee extensors) up to three years after the operation. Slightly more than half the patients
regained most of the size of their hamstring muscles (knee flexors).
Even after three years most of the patients had a difference in the size of their thighs. Very few could regain the full strength in the operative leg. A more aggressive training program is advised. Talk to your doctor about your concerns.
At two months after surgery, the lack of muscle bulk isn't as worrisome as if you were two years post-op.