Goodwillie left Tannadice for Ewood Park in August 2011 but has failed to nail down a regular spot in the Rovers attack and spent an unsuccessful spell on loan with Crystal Palace at the start of last season.
United boss Jackie McNamara would like to bring the 24-year-old back north of the border but is unsure of how the as-yet fruitless negotiations will conclude.
He told Sky Sports News: "We made an approach to Blackburn. They said it wasn't enough, so that's where we are at the moment.
"If we go back in, we'll see. We have got other targets we are trying to pursue and hopefully we can get the right ones in.
"I think he's a very good player but there has to be a line as well.
"It's a loan. It's different if you're buying someone and they are going to be an asset to your club.
"He's a fantastic player and I would like the chance to work with him, but he's not our player. You can only try. So far it's not been successful."