Stanton has apparently been available to pinch-hit over the last three games, but clearly, his quad isn’t going to allow him to play in the outfield during this series. Boone pretty much confirmed that before Game 4 when he told the media that Stanton wasn’t an outfield option, but he could be ready to be the DH in Game 5 on Friday. From the Yankees standpoint that’s good enough of a reason to justify keeping him on the roster, but that’s certainly debatable.
If this was the regular season there’s no doubt Stanton would have been placed on the IL but now if the Yankees replaced him on the roster he’d be out for the World Series as well.