From a 2016 ESPN article,

See article here

Paul Pierce on retiring Chuck Coopers jersey-

Why not?" Pierce, now with the Los Angeles Clippers, told The Undefeated. "There are probably a lot of numbers up there that shouldn't even be retired. You've done something groundbreaking, and you changed the course of history of bringing black players to Boston.

"His picture should be up everywhere, and his number should be retired. It's surprising it's not."

Cooper was the first African-American drafted in NBA history when the Celtics chose him in the second round on April 25, 1950. Then-Celtics owner Walter Brown famously said he didn't care whether Cooper was "striped, plaid or polka dot," after he was drafted. The former Duquesne University star joined Nat "Sweetwater" Clifton and Earl Lloyd as the first blacks to enter the NBA when the 1950-51 season arrived. Clifton and Lloyd are already members of the Naismith Hall of Fame.

But Cooper isn't. At least not yet.

"I'm not sure why," Chuck Cooper, Jr., told The Undefeated.