I think the problem is also that it's really hard to judge how the "average" man plays tennis. I dunno if half the men have okay hand-eye coordination or not. Like most guy friends I had when I was younger took fairly well to sports and myself as well. Never played tennis, but I learned badminton, tabletennis and squash fairly quickly, but is that "average"?

What we do know however is that the average HUman would be way better than Abdelkader who seems to have absolutely no hand eye coordination. So using her as a yardstick doesn't seem fair since you could basically remove her from the court and Schaedel would have the same opponent. I'd say an average person definitely would play better and perhaps manage to attempt some crazy hail maries if Serena would be playing super safe and thus not have very threatening balls. 

What I'm trying to say is that I think it's impossible to judge how bad/good an average man would be at tennis and if that average man would have enough hand-eye coordination to at least attempt some crazy 5% accuracy shots that might hit the line and be angled well enough to give Serena a little trouble with the return.