I would think if his clutch nut was coming loose he would feel the slack in his clutch cable when he pulled in his clutch handle. When mine came loose if you rev-ed the motor the handle would move back and forth depending how the nut spun...
In the end trying to get home, it "clutch basket" backed out until it hit the inner primary and put some nice grooves in it...
It sounds like the throw out bearing to me. Either way he is at the clutch basket.. Check or change your transmission fluid while you are at it and see if it is milky or contaminated with water.
Neil