Details of the bid are yet to be announced, but Ferguson is currently undergoing a medical (Mon 20:45) at Ibrox.
Wantaway Ferguson handed a written transfer request to Mark Hughes earlier this month which was accepted by the Rovers board on the condition that they would only consider bids of at least £6m.
Earlier tonight a former Rovers target, Craig Bellamy, signed for Glasgow Celtic on loan. It is thought that the signing of former Rangers favourite Ferguson would settle the fans, rival the signature of Bellamy, and help Rangers push for Scottish Premier League title.