Bradley was carried off during the second half of the JPT defeat to Sheffield United and is expected to be out for upto four months.
He had done well having been asked to fill in at centre half with the Millers already struggling due to a lack of bodies in that area.
"Mark saw a consultant yesterday and is going to have an operation on Tuesday. He's done a lot of damage to the shoulder so getting the operation done now is probably the most sensible thing to do", said manager Andy Scott talking to Millersplayer.
Earlier today Scott confirmed his search for loaness to strengthen the squad but insisted he won't be rushed into finding quality replacements.
Captain Ryan Cresswell is out with ankle ligament damage whilst Troy Brown is away on International duty, leaving Michael Raynes and a returning Johnny Mullins as the only recognised fit centre backs at the club.