Scott told the clubs official website that the striker hasn't been pushing his regular strikers often enough, despite fans calls for the 24 year-old to be more involved.
"I spoke to Brian McDermott at Reading and obviously Brett's situation was he was mainly featuring from the bench and from our point of view we felt we needed someone who was going to push our front two a bit more.
"Brian understood that and they were happy for him to go back and they are looking to get him out on loan to somewhere where he will play more regularly.
"We appreciate the fact that Reading loaned him to us in the first place. Brett was great to have around the place and we wish him well for the future."
The Millers will now be looking for more attacking options in the loan market after the sale of Chris Holroyd to Preston.