Well TMZ has just given sort of an answer as to why Bobby Brown didn't show up to perform last night with New Edition at NRG Arena.

According to TMZ:

Bobby Brown has decided he just can't keep up with the boys ... because TMZ has learned he has now quit the New Edition tour ... for medical reasons.

Bobby was struggling to perform with his group in Mississippi last week ... huffing and puffing and eventually leaving the stage altogether.

Now Bobby's people tell TMZ ... the singer had "an intrusive medical procedure" and needed to go under the care of his doctor, making performing impossible.

We're told he was exhausted and fatigued and could not go through the motions on stage.

Bobby says, "I apologize to the fans of New Edition.  I really wanted to be with my brothers, but presently I am unable to give the fans what they typically expect from New Edition."