The ex-linebacker made the inflammatory comments on a recent episode of his podcast "The Pivot," where they were talking about the Broncos QB and his wife ... whom Crowder apparently feels is in the wrong relationship, invoking her ex of several years now.

We'll let CC speak for himself here, because he says a lot ... and much of it is pretty mean. He calls Russ a "square" and speculates Ciara is only with him for cash.

He also theorizes there's just no way Ciara would ditch someone like Future and get with Russ -- who's seen as his polar opposite -- unless there was something deeper fueling her ... because he thinks all women have a type, and believes Ciara's shown her cards.

On Sunday, Crowder doubled down on his "goofball" jabs -- posting an old photo of Russ at the NFL draft in 2012 next to his then-GF Ashton Meem, whom he mocked in the pod.

Of course, he got strong pushback from his fellow podcasters ... who tell him that women want peace, and that Ciara and Russ are perfectly happy together -- as they've been married since 2016 and have kids together.

Sooo, it seems the proof is in the pudding here ... namely, the fact they've stayed together this long proves Crowder's train of thought isn't actually supported by reality. Russ and Ciara have been couple goals for a very long time now -- and yet, this narrative persists.

Russ, meanwhile, appears to have responded to all the renewed chatter ... albeit cryptically.

He tweeted Sunday, "'But the fruit of the Spirit is love, joy, peace, forbearance, kindness, goodness, faithfulness, gentleness and self-control. Against such things there is no law.' Galatians 5:22-23 NIV."