O'Brien pens new Us deal
Nottingham Forest are set to hold talks with Millwall striker Darius Henderson.
Henderson is expected in Nottingham on Thursday after being told he can leave the Reds' Championship rivals on a free transfer.
The 31-year-old, who has scored seven goals this season, is one of the higher earners at Millwall and is also out of contract in the summer.
Lions boss Kenny Jackett is keen to get Henderson off the books at The Den in order to free up funds for new players.
"Henderson has been given permission to speak with Forest and this will happen on Thursday," Millwall director Peter Garston told South London Today.
"The decision to allow this to happen was purely Kenny Jackett's. He was under no pressure from the board and Kenny is in total charge of team matters.
"Henderson leaving will free up wages. Kenny has targets and will go for them when he is ready and get who he wants at the money he is willing to pay, but he won't rush into it."
Henderson has not scored for Millwall since the start of November - against Forest as the Lions won 4-1 at the City Ground - and he has been in and out of Jackett's side in recent months because of injury.
The 24-year-old left-back, who has made seven appearances for the U's since signing in September, put pen to paper on a new deal on Wednesday.
With Liam Davis out for up to a month with a hamstring injury, the former Bradford and Exeter defender will continue to provide cover for the left side of the U's defence.
"I'm really pleased to have signed," O'Brien told the club's official website. "I have thoroughly enjoyed my time at Oxford. The fans are excellent and we have worked very hard as a team to get into a good position in the league.
"I am looking forward to playing a part and trying to carry that on. We have a tough game at Fleetwood on Saturday so right now I am totally focussed on helping the team get another three points."