Which Roger Federer will we see when he comes back?

Roger Federer's injury-plagued season took a turn for the worse Tuesday, when he announced he will take the rest of the season off to further rehab his ailing left knee. Given what we saw at Wimbledon, the way his legs seemed to give out in the [Milos] Raonic match and how fast he came back from knee surgery earlier in the year, it's not all that stunning. Since the knee surgery back in February, he's been at-risk.