This might be a controversial view, but I actually thought they improved when Henderson went off. But I get your wider point totally.
What would really worry me if I supported them, is these injuries are now getting repititive for players, and they are not of an age where they get over them, Remember Mirallas, pinged a hamstring and was really never the same player again. If it's 3 months it's obviously a serious tear, that occurred when he tried to carry the ball forward.
What the consequence would be, is either it will go again the next time he tries to run forward at pace, or he will just look to avoid doing that for fear of it pinging again (when muscles tear, unlike bone they tend to recover weaker, with scar tissue, especially bad tears). It's like Delph with us, once he started getting injured, it just becomes repetitive. I doubt he is going to be able to play at the top level again for any period of time.
They seem to have a number of players like that now. I'll keep saying this, but he just hasn't rotated his squad well enough. They seem to come in and he sticks with the same 11 until the player breaks down. You should be aiming to rotate before you hit the crisis point of a major injury, epecially with older or more injury prone players.
Mark my words, Keita will have a good sub appeareances, be thrown into starting games, then start every game, be overused, then break down again.