22-year-old Haley, after penning an emotional goodbye letter with her twin sister Hanna in April, has decided she won't hang up her Nike's after all ... she's entered the transfer portal and plans to play again starting next season.

Cavinder's last run on the court was epic ... she helped lead the Univ. of Miami women's basketball team to their first-ever Elite Eight. The Cinderella run included an upset of No. 1 seeded Indiana, a game Cavinder iced with clutch free throws in the final seconds.

Haley earned second-team All-ACC honors that season, averaging 12 points and four rebounds.

Aside from the success on the court, Haley's also a star away from the hardwood ... counting nearly three-quarters of a million followers on Instagram.

Haley and her sister Hanna also signed an NIL deal with the WWE as part of its inaugural "Next In Line" class. Many fans expected them to join the pro wrestling powerhouse as the next step in their career.

Adding to the surprise of Haley's decision ... she made it clear she didn't want to play without Hanna, saying, "I started with her, so at the end of the day, I want to end basketball and start our new lives together, but it was definitely difficult for me."