Could be a problem with the lower leg muscles, try checking for trigger points along the front of the shin:
http://www.triggerpoints.net/triggerpoints/extensor-digitorum-and-hallucis-long.htm
Diagram shows the areas to look and the site of referred pain (onto the top of the foot)
If you find one it will be very sore. Short very firm massage strokes in one direction over the point, about 10 times repeated 3-4 times daily should help.
If not, then it's something else....