Ricky - A tennis ball could skirm through the grill or even bounce and hit him in the jaw - causing injury. Would you want your professional at your club doing this before the start of the season? Not sensible if you have to line up a sub-pro week in week out that you can ill afford until he recovers...
Skiing is fun - but footballers aren't allowed to ski because it's deemed a risk. IMO this is just as bad.
are you for real? a tennis ball might give him a bruise, not much more
and yes, i have been hit by a tennis ball, a full-blooded serve into my cheek, it stung like (No Swearing Please) and i had a massive red mark, that was all
and i think a club can cope without a pro for a few weeks