Turns out it was exactly as bad as feared. Danny Welbeck, injured in Sunday's Manchester City match, had knee surgery today and is expected to undergo a nine month recovery process. It was already thought he'd miss the European Championships this summer, but this now puts his recovery and return back to February of next year.
This sucks. While Welbeck hasn't ever been the 20 goal a season scorer I thought he'd be when he arrived, he's been a very solid contributor when healthy; the fact that he's recovering from a similar injury to his other knee that just saw him return to action in February of this year is just an extra cruel layer of disgusting icing on a cake that is made of fish guts and expired mayonnaise.
(8.35AM PT EDIT: added context)
Apparently, as a kid Welbeck suffered from Osgood-Schlatter, a disease of the knees that is extremely painful and can hinder growth and development of the joint. I don't know if this has any impact on the knee problems he's had as an adult, but reading about him being in agony after training as a kid is not great.
So, I guess all we can say at this point is get well soon, Danny, and hopefully you'll be able to contribute to Arsenal's title run next season.