The cause of Orr's death is currently unclear ... but it was recently revealed the basketball player and coach was in hospice and not doing well.

Louie starred in the Cincinnati area as a high schooler before heading off to Syracuse where he played college basketball for four seasons under Jim Boeheim.

After Cuse, Orr entered the NBA Draft, where he was selected in the second round by the Pacers. Louis spent two seasons in Indiana.

Orr resumed his professional basketball career in New York, playing six seasons with the Knicks. Louis was teammates with Patrick Ewing ... whom he later coached with at Georgetown.

Orr averaged nearly 10 points and 4 rebounds a game over his NBA career.

Louis went into coaching in the early '90s, serving as an assistant coach with stops at Xavier, Providence and for JB at his alma mater, Syracuse.

After coaching one year at Sienna in New York, Orr was hired as the head man at Seton Hall University in South Orange, NJ ... replacing Tommy Amaker, who'd just bolted for Michigan, following a terribly disappointing season.

Orr brought back stability and respectability at SHU -- twice leading the Pirates to an NCAA tournament birth -- including during the 2003-2004 season when his team beat a stacked University of Arizona squad in the first round.

The basketball world is mourning the loss of Orr ... with former players, coaches and teammates expressing sorrow over the loss of not just a good coach, but a good man.

"So heartbroken with the news of Louis Orr's passing. My first Syracuse recruit n Knick player was as kind a person to play in the NBA - our thoughts and prayers are with his family," Rick Pitino wrote.