I over did it running a couple of weeks ago and have had constant soreness and tightness on the top of my left foot, from the middle right back to where it meets the leg/shin. The injury is also causing my left calf and outer shin to be tight and some soreness on the bottom of my feet. The pressure in the top of the foot where it meets the leg is quite sore when I try to walk. It's not a stabbing pain, more like a dull ache, like something hard pressing when I raise my toes.
I've read a bit about extensor tendon injuries and mine feels similar, though the descriptions I've read seem to show the tendon pain being only in the middle top of the foot, not where the top of the foot meets the shin bone.
Unfortunately, I have flat feet and also some nerve damage to my lower left side, which no doubt contributed to this injury. The nerve damage left me with a bit of drop-foot, so there is more stress on the tendons.
I've had sore feet in the past, but it usually heals after resting for a few days. So going on three weeks is making me a bit concerned.
I did see a doctor. She had me go up on my toes and bend my foot back, which I could do. She seemed to think it was a soft tissue injury, but didn't offer much in the way of treatment except rest. I kind of wished she'd sent me for some imaging.