go to the doc, if it’s an achilles it may require med attention
I did exactly the same about a month ago (jogging across hockey pitch I felt something hit me on the back of the leg, then I had to sit down), it was actually my muscle going, I’ve ripped my left gastronemius (calf) – for me the med diagnosis was 1 month without use, then I could start light exercising then back to sport after 2 months (*ish) – I actually started unclipped in, mainly right leg, unclipped in, on the flat cycling after about 3 weeks. FYI it took me about 1 and 1/2 weeks to do stairs properly – all weight on legs with foot flexing.