why does he still have swelling after another season out? get the vet in and find another LB to help zinchy
Pure guesswork on my part:
as I understand it, rehabs after knee ops can be hampered by a muscle imbalance and subsequent issues on the CNS level. For example, if you're underloading the joint after surgery and use it 'incorrectly' for a long time, you will have wrong motor behaviour formed, which is very difficult to get rid of. The longer the rehab, the higher the likelihood of such deviations.
Your knee might look healthy, but under heavy loads the imbalance shows itself, causing microtraumas of soft tissue or, worse, affecting important joint structures (meniscus, cartilage, etc.). I've had a difficult rehab after ACL plastics myself and seen people with such problems. These issues are difficult to fix, most likely City have decided that club doctors aren't qualified enough, and Mendy needs daily workouts with 'narrow specialists', hence his voyage to Barcelona clinic.
As for his swelling, I think it just indicates he trains a lot trying to solve the issue, 're-tuning' his joint. Minor injuries and swellings here and there are part of the process.