Robson however has urged the left-back to stay with the Magpies, and says he has evidence another Premiership club - named as West Ham in Friday's Guardian Newspaper - has made an illegal approach to sign the Frenchman.
It is claimed that the club contacted the player without first getting the club's required permission.
"We know he has been tapped up by another Premiership club, and we will be reporting that club," claimed Robson.
"I will not say who the club is because i intend to conduct this through the proper channels but I feel very strongly about this."
Bernard joined United on a free transfer from Lyon two years ago.