"The club will be making no further comment on what is now an ongoing legal matter."
The National Crime Agency (NCA) said on Sunday it had launched a second probe into alleged match-fixing in English soccer after a Sunday newspaper claimed a player told an undercover reporter he could guarantee certain events in a Championship match.
The NCA confirmed on Sunday that six people had been arrested following the Sun on Sunday investigation.
Striker Campbell, 32, played for Blackpool and Queen's Park Rangers in the Premier League before joining Blackburn in July.
The Sun on Sunday said it had evidence of a player saying he arranged a booking in a recent Championship match in which another received a 30,000 pounds ($49,100) payment for getting a yellow card.
The same player allegedly boasted he could also "rig" Premier League games.
In a separate match-fixing investigation, four people have been charged, including two players from an English sixth tier semi-professional team, in connection with an alleged international illegal betting syndicate.
Michael Boateng and Hakeem Adelakun, both 22 and from Whitehawk FC in Brighton, along with Chann Sankaran, a 33-year-old Singapore national, and Krishna Sanjey Ganeshan, a 43-year-old with dual UK and Singapore nationality, were charged with conspiracy to defraud contrary to common law.