Glen "Big Baby" Davis says Zion Williamson needs to lose weight ASAP ... 'cause he tells TMZ Sports being the same size as the Pelicans star cost him his NBA career!
"That’s one of the reasons why I stopped playing was because of my weight," Glen says.
Davis says he was just too damn heavy during his playing days at around 289 pounds ... and blames the weight for 2015 ankle and foot issues that ultimately ended his NBA career.
Now, he's sending a warning to Zion -- who's listed height and weight (6'7", 285) is nearly identical to Davis' when he was playing -- saying Williamson's gotta drop some pounds.