Agree with the above rolling comments. In addition, aggressively roll your quads and ITB. Remember that one of the four quad muscles crosses the hip, effectively acting as a hip flexor. If the quads are loaded with adhesions your hip and / or knee will eventually feel the effects from it. The small Orb ball, a softball and the rumble roller are my preferred quad rollers. Re: stretching, the couch stretch is the best for the hip and upper quads. Place the affected side knee into the corner of a chair or couch, with the unaffected side foot on the floor. Then make yourself tall from the knee to rib cage and feel the length through the whole front area. Then just fine tune with a little rotation away from the affected side. This stretch is great for identifying length / tightness imbalances from one side to the other as well. Good luck.
Thanks for the insights, very helpful!
"I was tired, so I shut off my brain and my body finished without me"
~KFU, age 13