I am not sure how or whether Alsa bus offers a thru ticket from Leon to SdC. However, Alsa offers Bus service from Leon to Ponferrada, and from Ponferrada to SdC. There is a stop in Pedrafita.
There Is also train service from Leon to SdC
You indicated that you want to walk slowly due to injury? Suggest you take bus to Sarria if you can’t negotiate hills.
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