I've had this exact tendonitis situation after overuse in training routines - granted i am considerably older and not an all world athlete - but it was from working out nonetheless.
For me it was a three-month recovery. Every morning it felt like it was back to square 1. Going downstairs was ridiculously difficult. I could not imagine being an RB with even a hint of it. Doesn't matter how tough or gifted one is, if your soft tissue isn't working, you ain't either.