I'll give my 0.02 here and people can take it for what it's worth. I'll be the first to say I haven't examined him so this is completely spit balling (don't want the usual posters to think I'm trolling or point out the obvious that I am speculating. I'll admit that right here and there. And for the record, I don't care about the Vikings or enjoy "trolling them"... I was high on Bradford after the preseason and have said many times the Vikings will be in the running for the division. I'm not a die hard NFL fan that trolls his team's rivals on an online message board when their players get hurt. Only Jay Cutler when he was on Chicago though... because he was a "kitty cat"). Sad that I need a disclaimer but here we go!
Let's talk about the usual suspects, starting with the least worrisome.
Scar tissue: Not buying it. Scar tissue was there a week ago, 2 weeks ago, 2 months ago. It will be there tomorrow, next week, the week after. It's not something you rest and it goes away. Unless the scar tissue was inflamed... then I'd be even more concerned because then you're talking about the same issue week by week. What changes between week 1 and 3? The scar tissue is still there. Still a potential problem
Pulled muscle: Unlikely given it's his "knee." If it was his hamstring they'd say hamstring, or quadricep if it was quads. Also they wouldn't do an MRI
Bone Bruise: Possible. This would result in swelling and pain. A week or so off and it'd be more tolerable these take a while in general to heal. This seems very reasonable
Meniscus: Likely not the issue, but possible. They said no tears so if this is torn then they are lying.
Ligament Strain: Also possible. They said no tears, but it doesn't mean he could have a significant strain, which would impact his ability to drop back and pivot on his knee. This wold take a few weeks to get better
ACL/PCL/MCL/LCL tear: Not likely given their own report.
Cartilaginous defect: This is also a possibility. This is what I'm suspicious of. Something that causes a lot of swelling and impaired ability to run, cut, pivot, weight bear. Usually this is a swelling/pain tolerance thing, but it can get worse if it's peeling away from the bone and this would possibly lead to a microfracture or another less-common-for-NFL-player-type surgery that I won't get into. This is what I'm suspicious about given his symptoms and how vague the Vikings have been with actually coming out and saying what is wrong with him. They just call it a "knee." Okay. If it was something not very serious such as a bone bruise they'd likely just say it. That plus his sx make me think this is a pretty big deal and they are hoping they can avoid anything season ending. If it's not getting worse it's just a wait and let the inflammation go down, but it's not going away either in that case. Sucks. As a Diggs owner I was buying this offense and relying pretty heavily on it. Hope it's nothing big, but I can't help but see this as a likely possibility