The Back the Bairns consortium of fans, business figures and sponsors, led by David White and Kenny Jamieson, was one of three groups looking to take control, buy the Major Shareholders Group shares and invest more money into the club.
However, the board unanimously named Campbell as the preferred bidder after hearing his sales pitch. There was reportedly an Indian consortium led by former striker Alan Gow also interested.
Back the Bairns though have raised concerns about the move to make Englishman Campbell the preferred bidder after finding out information about the 46-year-old.
A statement from the group said: “After conducting background checks and meeting Mark Campbell, we confirm that we identified information we believe is potentially of concern to the club.
“We have notified the MSG/Board of our findings and asked that they are fully investigated via due diligence.”
A Falkirk statement said: “Two other bids were received, including a well-researched and well-presented fan ownership proposal which was detailed and impressive, but did not match the exceptional vision and the financial strength of the proposal the board is now considering in detail.”