If you're playing football while trying to recover, it is long term, because you reinjure it every time you stress it. Especially if you're blocking a 280 lb defensive end 60 times a game.
I strained an oblique years ago, a non-sports Grade 1 injury, and it took me months to recover. It was one of the most limiting injuries I've ever had; a person just does dozens of things every single day that aggravate it, and you just can't avoid reinjuring it. Getting into your car, getting out of your car, getting out of bed, rolling over in bed, putting your shoes on, sitting down on the couch, getting up off the couch, bending forward and reaching into the refrigerator, putting a T-shirt on, and on and on and on.
Based on what I've read, and my own experience, I'd guess that for a tackle, probably a couple of months, and even then he'll have an elevated risk of re-injury for some period of time. I've never known of a tackle who had this injury. And it sounds as though his is a lot worse than mine.
I do know of a few college and NFL quarterbacks who were able to play through it, at least for a while. Mac Jones played through it yesterday, in fact. He was injured last week, but I don't know how bad it was. I think that'd be a lot easier than playing on the line.
I hate to be all doom and gloom and the sky is falling, but I don't see any way this isn't a serious problem for a big chunk of the season. I sure hope I'm wrong, though.