Posterolateral leg pain, Case Study 1

Hay guys, just wanting to ask for some advice.

I have a client who came to me with the following issues:

Lateral knee and hip pain following 200m of jogging.

Diagnosed as ITBFS (3 weeks ago)

I have treated his muscle imbalance, corrected his running and gait patterns, given him stretches and exercises etc. corrected his Lx. instability issues following a previous injury... All of which has greatly improved his condition.

He now has no lateral knee or hip pain.

However... since his symptoms have cleared, he one day found that (approx 5 days ago) he gets a sharp posterolateral pain in his leg. The pain is ONLY evident during running. It's onset is immediate (first step), during stance phase, is constant VAS of 4/10 regardless of running distance, and disappears immediately on stopping.

He gets no pain on any active / passive exercises, SLR L=R, neural glides are all negative, MMTests are all negative. The only representation of pain I can get is tenderness over the area (requires me to almost get medial and under the biceps femoris muscle bulk before being able to localise the site) The location is approx 2/3 down his upper leg slightly medial to his biceps femoris. He does not feel it during any ADL's. I have tried stretches/releasing hamstrings, altering mechanics to isolate the symptoms, testing straight up, testing following warming up / massage, neural glides/Lx and piriformis work then retesting, even tried compression bandages, bracing... he still gets the exact same 4/10 pain, immediate onset and relief.

I am currently looking at his hip stability and trying to improve his lumbar / hip mechanics, was thinking possibly referred pain due to increased compression to his Lx. or maybe overactivity / further mechanics I may have missed during stance phase loading which may be giving referred pain. He # his lumbar vertebrae (L3/4) a few years back, but is very active and has no Lx. pain / problems currently, was given good rehab / exercises which he has been slack at recently.

Just after some ideas of possible alternate diagnosis? Was thinking possibly some further medical investigations to give me some more information. Am I missing something very obvious and common!?
Thanks!