Nel clutched the back of his right leg while batting in Surrey's second innings, in which Mark Ramprakash narrowly failed to become the first player in the country to score 1, 000 runs.
McCullum, who overcame a painful collision with Johan Botha when he slid into the crease and injured his neck, hit two sixes, top-edging over fine-leg and flat-batting over long-on.
Saj Mahmood (30 not out) produced some lusty hitting to earn Lancashire a batting point before James Tomlinson trapped Gary Keedy leg before to wrap up the innings.