What is troubling is the length of time it's taking for a diagnosis. The only other time I've seen this is with degenerative arthritis and a microfracture of some kind. Let's hope it's not microfracture which means he's gone for the season and perhaps it could be a career-ender depending upon the severity.
On the flip side this could open the door for Jonah Williams who has the prototypical size and speed to play DE. IMO Brockers is the most likely candidate to move inside to 1 T to replace Robinson who will or will not return this year. SJD proved to be a swinging door in the middle last year. Gaines is looking more like a 3 T as his best fit. The Rams also have Michael Hoecht who can play a 1T. He has the physical metrics, strength and the quickness to be a very good long term option to Robinson at NT.
Okoronkwo IMO lacks the speed and size to play OLB in a 3-4. They could move Ebukam into that outside spot opposite Floyd as well though it would open a spot at SAM. Okoronkwo lacks the size and speed to play at SAM but Williams does have those qualities though I'm not sure he's been coached up to play there.
As bad as this looks, and let's be clear it is a big loss, the Rams have options. This is turning out to be a very bad TC and off season for the Rams. But this roster is deep with talent albeit inexperienced. IMO Hoecht was signed to be the long term solution at NT to follow on after Robinson who IMO won't return. IMO it was an undisclosed injury which voids the contract and Robinson is no longer shown on the roster.
One thing about Hoecht is that his combine numbers were eerily similar to AD's. His physical metrics make him a perfect fit at 1T and his quickness will make him a mismatch for most centers. It's why I think the Rams made no move to replace Robinson.
One thing is coming clear to me. As good as I think this draft is, I think their UDFA signings are equally good.