I agree with the above posters that this is a non-compelling reason for a drop in grades.
My D had a spinal fusion for scoliosis the summer between junior and senior year. She took 4 AP classes senior year and completed all the summer homework despite not being able to think clearly due to pain meds for a couple of months. She also participated on her school’s water polo team. She couldn’t play but still attended all practices and games, assisting the coaches.