i get tight in that area too along with right above your front pockets on a pair of jeans.
for the area you are talking about, get a lacrosse ball or softball/baseball and place it in that spot. roll it out side to side and just hang out in any tight areas. if possible, when you find a spot hang out there and try and bring that knee up as high as you can. do that for a couple repetitions. also if you have a band, put the lacrosse ball in that area the best you can while laying with your back flat on the ground. take the band and loop it around your foot. bring your leg (while stiff) up as high as you can, get tension on the band, and bring your leg back down the the ground and hold for 3 seconds. do 3-5 reps each side