David O'Leary has admitted that Aston Villa are vulnerable at the heart of their defence with only rookie Gary Cahill currently available able to step in if either skipper Olof Mellberg or Liam Ridgewell are sidelined.
O'Leary opted to give Cahill, who spent a successful spell on loan at Burnley last season, a run-out in last week's Carling Cup tie at Wycombe to give him first team experience should he be required for the Barclays Premiership.
The knee problem which has ruled Martin Laursen out for the remainder of the campaign leaves O'Leary keeping his fingers crossed Mellberg and Ridgewell escape injury for the forsseable future.
Mellberg was rested for the Wycombe game with a tight hamstring although he did return at the weekend for the league meeting at Chelsea.
O'Leary told PA Sport: "I had to give Cahill some experience at Wycombe because if I lose either Ridgewell and Mellberg he has to play because there is no-one else to play there at the moment. I had to put him in the other night because we have got to give him some sort of experience.
"It was a hard game for him to come into and I know by him learning he can make mistakes but it has to be done. Mellberg had a tight hamstring last week and I didn't want to play him at Wycombe unless things really went wrong on the night and risk losing him for six weeks. He came back in at Chelsea but we are vulnerable in that position at present."
O'Leary's concerns may ease slightly once right-back Mark Delaney returns to first team action after his knee problem because he can also play at centre-half - a role he occupied at times last season and also for Wales.
