I'm just curious...

I can't see why he couldn't. The restrictions are NCAA and "club" baseball is recreational and not governed by the NCAA. Maybe the “club” has rules that would eliminate a professional but I doubt it. I can hear it now ---- “Hi my name’s Barry Bond and wondering if I could play on the club team while I attend Pharmacy School?”

THAT'S funny Fungo!

Actually, my son was in that situation. If it is a "club" team that plays club teams from other schools, you can't play if you played professionally. Apparently, there are rules that govern interscholastic club teams as well. They can certainly play in intramural baseball, however.