McMillan actually was on one of the multi-player rookie cards in the 1977 as a member of that inaugural Seattle team, but only ended up appearing in two games for the Mariners that year.
Over those two games he failed to collect a hit in five plate appearances, though played 10-innings of flawless shortstop over his four day September call-up.
He’d end up putting in another two seasons of Pro Ball in the Minor Leagues in 1978 and 1979, but would call it a career after that, finishing up in the Pittsburgh organization in Double-A, playing for Buffalo in the Eastern League.
But for those two games in September 1977, he was a Big League shortstop.