MICK McCARTHY admits Darren Carter's undoubted potential could stop the midfielder from rejoining Sunderland on either a temporary or permanent basis.

The Black Cats have lost the services of the young player after his loan move to the Stadium of Light was cut short due to an injury crisis at parent club Birmingham City.

The situation resembles the recall of flying winger Stewart Downing to the Riverside Stadium at this time last year in a bid to boost numbers by Boro boss Steve McClaren.

Downing had lit up Sunderland with a string of fine goalscoring displays and this time Carter has been influential in the club's rise to third in the Championship table.

McCarthy had made no secret of the fact that he wanted to sign Carter for a longer period of time and still holds hopes of taking him back to Wearside sooner rather than later.

If a new deal is to be struck then it needs to be done before December 31 and will have to be a longer term loan deal.

But the Sunderland boss admits that, like Downing, he may have seen the last of the Birmingham middle-man, who could go straight into the Blues starting line-up for the derby with Aston Villa on Sunday.

"We will wait and see how he does now he has gone back. I personally think he will be fine in the Premier League.

"I wasn't saying that to Steve a month ago - I was playing it down a bit - but I think he has lots to offer Birmingham," said McCarthy, who is sure to keep an eye on developments during Birmingham's four remaining games this month.

"Stewart Downing came here and impressed - he was a terrific loan signing.

"Darren was here longer. The two of them, just in the way they fitted in, were great. Darren has been an absolute pleasure to have around the place.

"Not only in terms of what he has contributed on the pitch but everything about his whole demeanour. If he didn't play, he got on with it and did his job.

"If he came on as sub he did well. If he played wide left, he got on with it. I can't speak highly enough of the lad.

"I hope he does do as well as Stewart (who is now on the verge of England honours), although I won't get him back if that's the case. If coming here has helped him and helped Birmingham, it has certainly helped us. That really is what the loan system is about."

Carl Robinson's return to fitness ahead of tomorrow's trip to Cardiff has given Sunderland a boost following the departure of Carter, while Matt Piper is another option for McCarthy.

Winger Piper has yet to make an appearance this season, having undergone major knee surgery in the summer. But he enjoyed another 45 minutes for the reserves on Wednesday night.

The £3.5m signing from Leicester two years ago has been blighted by injury since arriving and he made only 11 appearances for the club last season.

McCarthy believes the player has shown great determination to get his career back on track.

"Matt is hungry to be back, for sure. On Wednesday he was the one player who gave me something to smile about. For the time he was on, his desire to play was clear. He is desperate to get back into the first-team picture," said the Sunderland chief.

"He has changed since I've been here. When I first came to the club he had gone through that cycle of injuries and there was almost an acceptance that that was how he was.

"He has worked hard over the last 18 months. He is a different animal physically to how he was. He has worked hard in the gym and done all his graft and he has put the hours in.

"I just hope for him that it pays off because he deserves to get back playing."

Cardiff are still hoping to push through a deal for Darren Williams in time for him to play against Sunderland tomorrow.

Williams has been on loan with the Bluebirds but will be unable to play at Ninian Park - under the rules of the agreement - unless a permanent switch can be sorted out.

McCarthy admitted: "If Cardiff decide to make the deal permanent - to take him until the end of the season when his contract runs out - I'm sure he will play. If they don't, he is still registered with us and he won't be able to play."