Britney showed off her moves, dancing around her home workout area. She had MJ's "Scream" going while she flaunted her choreography ... and the whole scene could be a response to what her manager told us ... that Brit's just not ready to perform.
We can't tell if the clip she posted Thursday is new or a #tbt. She didn't use the hashtag, but her outfit looks identical -- right down to her necklace -- to one she wore in a March 2018 workout vid.
Either way, it seems like a clapback, because just Wednesday ... Spears' longtime manager Larry Rudolph told us she's not fit to return to her Vegas show, saying, "From what I have gathered it's clear to me she should not be going back to do this Vegas residency, not in the near future and possibly never again."