The former Leeds striker has not had much luck at Meadow Lane, suffering a number of injuries and has missed nearly all this season with a knee injury that required surgery. His best game came in a 0-0 draw with Stoke, but he was unable to take the form into the next game as he picked up an injury.
Whenever he has been fit, fellow forwards Paul Heffernan, Mark Stallard and Danny Allsopp have been in form, leaving Hackworth in the reserve side.
"It is a blow whether he has broken the leg or not," The Magpies boss told the Evening Post.
"It is still early days to say how bad the injury is, reports yesterday that he had broken it were premature.
"We are still waiting for the results.
"But we do not need to keep losing players in this fashion.
"Whether it is broken or not, he is looking at some time on the sidelines."