The whole transfer has been a mess from Forest's point of view. They bought him after identifying him as a player that could possibly step up from the champ to the PL, but still be of use if they went down this season. They paid over £10m for him, and then changed their transfer strategy to basically buying high value big names.
They've got too many players in their squad to register him and having now stayed up, they are looking for better players than O'Brien. Forest need shut of him, no other PL or championship club in their right minds will pay more than about £6m to £7m for him, because he's spent the last 6 months wanking his time away unsuccessfully in the MLS on loan, after a loan deal to Blackburn hit the buffers. The only way Forest can get out of this is by loaning him to a PL club next season and hope that he plays & succeeds at that level, before getting rid.
If he's available for loan next season, I would certainly have him for the LCM berth, and I would also loan Doyle back.