Dwayne Wade says it's a matter of when, not if -- telling TMZ Sports he knows his former teammate's jersey will hang from the rafters in Miami one day.

Haslem -- who was drafted by Miami in 2002 -- has spent his entire career with the org ... and is considered a Heat legend for the longevity he has with the team.

Of course, D-Wade and Haslem have a strong bond -- the two played together for the Heat franchise for a number of years ... winning 3 championships in that span.

UD postponed retiring this past offseason and signed on with the Heat for year 19 ... and even though the veteran doesn't see much playing time these days, his impact on the sideline and locker room is certainly felt by the players.

As for Wade -- who was in New York for the release of his new book "Dwyane" -- we asked him if he had any advice for players on the Phoenix Suns ... whose owner -- Robert Sarver -- has been embroiled in allegations of racism and misogyny.

"You know, I'm in ownership now," the Utah Jazz part-owner said. "I don't comment on other teams."