Vice chairman Dave Smith said: "We believe an illegal approach has been made by agents to two of our senior players, in a bid to persuade them to leave the club.
"We have taken advice at the highest level from football authorities to discuss the matter with the players concerned.
"We are now considering making an official complaint in the strongest terms to the Football Association. This type of illegal behaviour unsettles players and disrupts preparations for games.
"The manager is under no pressure to sell and will only do so if it's in the interests of the club. We want to hold on to our best players and strengthen the squad in a bid to get promoted this season."