Matt Barnes is Not Welcome at Derek Fisher's Wedding, Says Ex-Wife Gloria Govan

Matt Barnes will "absolutely not" be in attendance when his ex-wife, Gloria Govan, marries Derek Fisher ... so says Gloria, who claims the ex-NBA stars are still NOT on great terms.

Remember, Barnes congratulated Govan and Fisher after they got engaged back in April -- saying he's happy for the couple because his kids have grown to love him.

But Govan says the relationship between the former Lakers teammates is still not great -- and Matt's presence would be "really awkward."

"[Matt] and Derek aren't cool," Govan said ... "They're cordial. I wouldn't say 'beef' but they don't talk every week."

It's about what you'd expect ... considering Matt and Derek famously fought back when Derek began dating Gloria a few years ago.

Govan closed with some advice to Matt ... don't waste your time buying a wedding gift either, because "I will throw that gift away."