I don't know how much of it is the injury. I'd guess it's affecting him at least somewhat, but part of that is on his game, too. With the types of shots he takes, even the slightest injury could throw him off.
But let's also not look past the fact that the supporting cast has been pretty bad, too. Both Klay and Green haven't really been themselves in this series either.
I'd say it's just as much about his injury as it is them not hitting shots and their style of play with quick, questionable jump shots. When they're not hitting shots, then that style of play isn't going to win you games against top teams. Add in the fact that OKC has just destroyed their defense and Golden State just keeps making unforced turnovers, and it's justified to wonder what went wrong beyond the injury.