WWE's Seth Rollins -- HITS BACK AT JON STEWART ... I'll Beat Your Old Ass!

WWE superstar Seth Rollins has a NEW message for Jon Stewart -- BRING IT ON!!!

After the "Daily Show" host called him out in a smack talk video, Rollins responded on "TMZ Hollywood Sports" on Reelz and fired back at Stewart ... calling him old, frail and a total wuss.

We raised the issue that Stewart was a college athlete who played soccer for William & Mary ... but Rollins didn't seem fazed. In fact, he talked even more smack.

"People think WE take falls? Look at soccer players!"

There's more ... much, much more. Can't wait to see if Stewart hits back -- again.

Make sure to check out "TMZ Hollywood Sports" on Reelz -- weekdays 3 PM ET, 6 PM PT.