Chris Brown Says People Wish Quavo Died Instead of Takeoff

Chris Brown 's not fooling around in his beef with Quavo ... dropping a new diss track -- and invoking the name of Quavo's late nephew, and Migos star, Takeoff .

The singer-songwriter -- whose well-documented beef with Quavo's reignited in recent days -- put out his new track "Weakest Link" on YouTube and Instagram ... and, he's clearly going for Quavo's throat throughout the track.

And, one of his biggest disses ... "R.I.P. Takeoff, he the only real one, I got true respect / Crazy how when he died, everybody really wished it was you instead" -- so yeah, Brown's taking the kid gloves off.

And, it probably hits even closer to home for Quavo ... because he and Takeoff were together -- playing dice outside a Houston bowling alley -- when a man opened fire , killing Takeoff.

Quavo publicly mourned his nephew in the years since performing in multiple tributes with fellow Migos rapper Offset ... so, this blow feels particularly low from CB.

Brown's got other bars too ... in the song, he claims he had sex with one of Quavo's past GFs while she and Q were still together -- which, if true, explains a ton of the animosity between the pair.

It's not clear who Brown's talking about in the song, but many fans and reports are pointing to Saweetie as the possible subject of the line.

Seems like Quavo and Brown are pretty consistently competing for ladies ... remember, Chris rapped on his song "Freak" about Quavo hooking up with his ex Karrueche Tran -- and Quavo responded by bringing up Brown's violence against women.

Bottom line ... this beef's getting serious -- and, it's Quavo's move.