Lytham St Anne's-born American tycoon Daniel Williams, 30, has already declared his interest in buying Rovers - his boyhood club.
But Rupert, 57, is building a consortium and has tried to get Miami Dolphins owner Wayne Huizenga on board.
Asked whether he was interested in buying the Ewood Park club himself, Huizenga said: "That is not the case but I know what you are referring to.
"My good friend Johann Rupert asked me if I'd be a very, very small partner.
"I did say that I'd do that - but only because I was a friend of his.
"I personally have no interest in buying a team over here.
"I know some of our fellow NFL owners have come over here and purchased all or parts of teams and I'm really not sure what their agenda is."