MARTIN O'NEILL has been forced in to a transfer rethink after admitting he does not know if experienced defender Wes Brown will return to action for Sunderland this season.

O'Neill had been expecting to offload either Titus Bramble or Matt Kilgallon – perhaps even both – during the January transfer window which opened today.

But after John O'Shea picked up another hamstring problem in Saturday's 2-1 defeat to Tottenham, Sunderland will have to rely on both fringe defenders in the coming weeks.

It remains unclear the length of time O'Shea will be sidelined, but the only available alternative to Bramble and Kilgallon at the heart of the defence for tomorrow's trip to Liverpool is Carlos Cuellar.

The situation has been exacerbated by the ongoing problems plaguing former England centre-back Brown.

The 33-year-old suffered a set-back in early December when he had hoped to make his comeback from a long-standing knee problem. Now O'Neill is not even putting a timescale on a comeback and has told the defender to take time out just to get himself right.

“We have lost his services and it has got to the stage where we can't even consider him,” said the Sunderland manager. “The last time he played for us was pre-season. You can't believe that we are at new year and he still hasn't played. It's bad enough for us so it must be terrible for him.”

It will be a year at the end of the month since Brown sustained the knee injury during Sunderland's FA Cup win over Middlesbrough.

After not playing again last season he was on his way back during pre-season before breaking down again during the club's Peace Cup adventure to South Korea.

He then had a knee brace fitted in October before it was taken off last month, but now O'Neill fears the former Manchester United defender is still some time from a return.

He said: “Wes is feeling really frustrated with it all. He just has ten or so days where he thinks he is going well and then gets a set-back. He has had these injections, a course of sugar injections, which are making him feel better at the minute. He feels they are benefiting him.

“I will leave it with him and see how things go. It would be great if he could play again this season but he is pretty frustrated.”

With Brown's problem not going away and O'Shea sidelined with renewed hamstring trouble, O'Neill knows he needs Bramble, Kilgallon and Cuellar to shine.

That means the chances of either Bramble or Kilgallon leaving have seriously reduced, with O'Neill admitting now is not the time to be allowing players to leave at a time when he is considering defensive targets in the market.

“We can ill afford to let anyone go until we get some replacements in,” said the Sunderland boss. “We are short enough at the moment, if John is out for some time then we have three lads who can play there. Wes Brown is not going to be available for some considerable time, so ...”

Bramble endured a stop-start 2012 both through injury and off-the-field problems and he has only made six Premier League appearances this season, three starts.

O'Neill said: “I think you have to try to be as fit as you possibly can to play in the Premier League. In that aspect it is very demanding.

“Titus got a calf problem on Boxing Day last season and then the next time we saw him was the last game of the season. That's a long time for a stalwart player like him and it can take its toll.”

As well as looking in to taking New York Red Bulls attacking midfielder Tim Cahill on a two-month loan, O'Neill is also keen on strengthening other areas and defence is one of those.

But he has been encouraged by Lee Cattermole's progress from a knee problem. The Sunderland captain is ahead of schedule and is doing work on the training ground in the hope of a January comeback.

That said, though, O'Neill is also looking at recruiting in the midfield area, with Inter Milan's 21-year-old Joel Obi being touted around top-flight clubs.