Knee pain is a very common issue people face that affects their training and activities in daily life.
Prior to the onset of pain is often stiffness and it is at this point you should look closely at what is causing it and put a plan in place to change what is going on.
I see so many people with severe loss of knee mobility that could have easily been prevented if the correct action was taken early on.
In many cases the tightness is more to do with weakness and poor alignment rather than over use and the quads being too strong.
The tightness is merely a protective mechanism from the body to protect the knee joint from more harm .
Stretching does not change weakness or faulty alignment of movement.
Poor Foot, Knee & Hip Alignment Creating Stiffness
The first thing to note here is that it is never the knee’s fault. 
The knee is affected by the ability of joints above (hip and pelvis), and below (ankle and foot), and if there is a problem with one of these joints the knee struggles to maintain optimal alignment during movement.
The knee is caught in a crossfire and is dependent on these joints to perform their roles correctly.
If any of these joints are unable to work effectively it disrupts the optimal alignment of the knee and now it will be impossible for the knee to track correctly when the knee is fully flexed.
The inside of the patella is covered in articular cartilage designed to reduce the stress / friction that occurs in the joint created by the quads. However, if you lack the correct alignment of the patella, you can end up with increased stress within the joint usually on the outside or lateral part of the knee.
And eventually this stress becomes pain and known as patellofemoral pain syndrome! This is where you see people foam rolling on the outer part of the thigh, (ITB) to release this tension which may help to some degree.
However, on its own it will do little for it isn’t just tightness on the outside of the leg that can produce issues.
lack of mobility in the ankle can severely ruin the movement up the kinetic chain and rob the quadriceps of strength in movements like the squat. This applies to all types of postures and is very often a huge factor with knee pain. We will need to consider foot stability in line with this but for now to keep things simple just look at ankle mobility on its own.
The ankle must be mobile enough to allow dorsiflexion needed to align the lower limbs correctly and allow an even distribution of load to be placed through the powerful muscles of the legs. If the mobility is lacking here the body must compensate and create new methods of movement that eventually lead to weakness and dysfunction causing pain.