NBA teams might not wanna plummet for Michael Porter Jr. next year ... 'cause the projected #1 pick in the 2018 Draft says there's a chance he won't jump to the pros after his freshman season.

We spoke with the 6'10", 215-pound phenom about being the big man on Mizzou's campus ... and MPJ says he's not worried about the hype surrounding him and just wants to focus on what he does on the court.

The 19-year-old 5-star recruit -- who was coached by ex-NBA star Brandon Roy at Nathan Hale H.S. in Washington -- is at the top of every way-too-early mock draft for 2018 ... but Porter says he might not even put his name into consideration after his first year.

We also asked if MPJ would ever be interested in signing with the Big Baller Brand ... and his response is hilarious!