Marshall went on Instagram and challenged the Steelers superstar to make a car bet over who will have more receiving yards in 2016 -- Brandon's Porsche versus Antonio's Rolls.
So, we reached out to Brown ... and here's what he told us:
"He don't really wanna do that. He just wants some PR. He too old to be doing that."
Brown also noted, "The RR is about $100k up [from the value of the Porsche]."
"If he really serious, CALL ME ... I'll gladly accept. Don't Internet it."