Richards, 19, is sidelined for the next five weeks as he recovers from surgery and is intent on letting the knee heal properly after the operation in London last week.
"I had been playing with pain but it was getting too much, " Richards revealed in his BBC Sport website column.
"Physio Ally Beattie felt if I did not have it sorted it could get worse and keep me out long term.
"They told me what was happening on Tuesday and I whizzed down to London on the train on Wednesday for the operation at the Lister Hospital in Chelsea."
He added: "All they want me to do now is sit and rest. After that I will be back on the treadmill and building up the muscle that was lost.
"Then I will be in the pool and doing more running. It is important to come back steadily.
"I am all right though. I am not on crutches and my leg is fine to walk on. I can drive too."