Maybe I'm far too optimistic, but I don't think it lowers expectations significantly for his career since he's still relatively young and WR's generally have longer careers than say, RB's. Expectations are already rock-bottom for this season.
Microfracture surgery isn't directly related to his reconstructed ACL, although I'm sure that injury played a part in it as a lot of ACL injuries also result in torn meniscus.
IIRC, microfracture surgery is done to promote/inscrease cartilage growth in the knee.
If his most recent surgery was to clean out the knee, I can see him playing the rest of the season because of his competitive nature, and then possibly opting for microfracture in the off-season which would allow him to recover prior to next season.
Microfracture isn't the career-killer it once was and the procedure has come a long way in a relatively short time.
The surgery is minimally invasive (about 30 minutes and done through an arthroscopy) and it takes "normal" people about 4 months to resume intense physical activity. A professional athlete may, of course, take longer to get back to playing condition. The fact that Walker was able to come back very well from a much more invasive procedure and play at a high level gives me confidence that should he need microfracture in the off-season he could still return to being a productive NFL and FF players.
So if we take this report as gospel and he does, in fact, need the procedure he could be back in time for training camp. He might be a little slow out of the gate, but he could definitely play next season and it might even prolong his career.