How old is he? Should contact the Health and Human Services department to see if government has any funding for residual or Long Covid symptoms. Ask if they have insurance requirements thst his insurance has to abide by for continued care.
If his insurance didn’t terminate his benefits,
He absolutely needs an EMG/NCS to see if he has nerve injury due to entrapment neurpathy or lumbar radiculopathy. Especially if that leg is also weak.
If he can’t straighten his leg out due to a knee flexion contracture, the acute care hospital and rehab hospital may be at fault and responsible for his care to correct it.
Insurance Benefits don’t cover therapy forever anymore. However, if the therapy isn’t documenting correctly, it can get cut too. Or his insurance carrier is a douche canoe.
Where’s he located? Needs to see an Orthopedic surgeon or a Physical Medicine and Rehabilitation specialist If he sees a PM&R doc, make sure that they do EMG/NCS testing too.