First off - I am trying to get an appointment with a sports doctor, but it may be a few weeks. I’m trying to figure out if this is something where I just need to stop training all together, or if massage and ice would be enough and I can keep training.
TLDR
• There was no injury moment that I know of.
• It’s a sharp pain.
• It hurts only in the moment I point my toes up.
• It hurts the most at the very beginning of movement and then fades. If I point the toes up the pain will almost completely go away in about 4 seconds.
• It’s more on the inside of the back of the knee (closest to the other leg / right side of left leg)
• When I am done moving my foot all the pain goes away.
• If I massage my calf muscles there is a narrow line from my knee twords my ankle that hurts but everything else feels fine.
• If I push through I have full power - I can stand on my toes on the leg no problem
• The pain happens even if there is no weight on the leg
• So far stretching it helps reduce the amplitude of the pain when it happens. Resting makes walking hard
Backstory:
2 weeks ago I did a longer (5hr) ride with a 40min SS interval 1hr in. Nothing special, Iv’e done a lot of these. In the last hour the back of knee started having a sharp pain on each stroke as I straightened the leg.
I needed a rest week anyway so I took a few days off of it completely then did only z2 rides. After a week I didn’t feel anything out of the ordinary but kept on doing sub 2hr z2 rides only. On day 10 I tested it out with a 25min max effort and everything seemed fine.
2 days ago I did a 2hr training ride with 60min of 90% FTP SS intervals. All good - Nothing at all. I even did a minute sprint of about 180%. Today I was on a long ride that started with 3hrs of z2 and the pain came back a little bit. I stopped and massaged it. Then I did a 15min 100% interval and a 20min 85% interval back to back. The pain was kinda there, but I didn’t notice it until the last 10 min of the ride.
Now, It’s hard to walk unless I stretch it. Any ideas what it might be?
Could be some sort of overuse injury. Maybe this article can help. I had a similar pain caused by the old dura-ace pedals that were know knee killers. Had to get my foot out quick and twisted the wrong way. Took about 2 years to go away. Back of my knee hurts now just thinking about it.
Had something similar. Turned out a Bakers Cyst. The fluid built up in the knee couldn’t drain due to swelling in the joint. Pushed Motrin for a few days and most of the pain gone. I’m now taking Motrin as a preventative before long rides and before bed after the ride. Knee feels a lot better and I can train like I want.
Thanks all - I got a appointment for Monday so just waiting till then 
Update - Went to the doctor and they aren’t sure what it is but is very confident I’t not a tear or anything. They think it’s tendinitis or just overuse and that I need to go to PT and start some strength training.
Leg feels a lot better and I was given permission to stretch it (alleviates the pain a lot)
Baker’s Cyst or bursitis (swelling of a bursa sack)
Another update - My leg started to discolor in areas and swell, and the calf muscle hurts to touch it. I never had an injury or impact moment so they sent me in for a DVT (blood clot) check. They didn’t find one but they did find a deep venous incompetency in the common femoral vein. I’m being bounced around a bunch of doctors and we aren’t fully sure what caused it.
Right now about the only thing that seems clear is that is is not ligament related
Ask your MD if you think there are any signs of popliteus issues - a small and often overlooked muscle in the back of your knee.
Just another update.
Not much changed other than I do have a valve issue in the leg but they don’t think it’s worth doing anything about. They think it is likely the discoloration and swelling is more likely from a small muscle tear than an valve issue. But I have a follow up in 6 weeks to make sure.
My personal guess based on a few things is that a nerve issue in my foot (Neuroma) was acting up had me pedaling in a way that caused the injury. I was trying to take pressure off the ball of my foot due to pain (I’m also seeing podiatrists to get this sorted too). I think maybe I ended up tearing some small muscle in the process.
PT is still unable to recreate any pain twisting the leg and what not and the knee seems good.
I do have some weak non-cycling muscles (some hip flexors, hamstrings, etc) so we are cross training now to strengthen them up in case that helps.
But generally the consensus is 
I’ve been eating like I haven’t reduced my TSS (I’m about 50% of pre injury) and doing some harder riding just to try to keep as much fitness and muscle as I can. Seems to work ok, but Iv’e found my mental strength and motivation to train hard have decreased the most.
I’m doing a 53mi ride this weekend. That was previously a short weekend ride but it will be my longest in 5 weeks - I guess we’ll see what happens.
Final update I hope
Test results showed that I did have a minor vein issue but they don’t think that’s what caused the discoloration and swelling. They think somehow I tore a muscle enough to cause internal bleeding and swelling. But right now it’s been 2mo everything seems to be healed, and all the evidence is gone
I look forward to getting back to training