Simon Grayson has ruled Darren O'Dea out of tonight's Elland Road clash with Blackpool.The Republic of Ireland international was withdrawn from the action during Sunday's game against Cardiff City after suffering with dizziness and blurred vision."Darren won't play on Wednesday," confirmed the boss. "He was suffering with dizziness and blurred vision on Sunday and is seeing the doctor."He had taken a bang against Birmingham - it wasn't concussion, it was dizziness - but he was given the all-clear by the doctor and he declared himself fit. He took another knock on Sunday and we brought him off."Head injuries are something you have to have take very seriously so he won't play on Wednesday and he will be a doubt for Sunday. He is the Republic of Ireland squad after that and obviously he will be very keen to play so we'll all be guided by the doctor."O'Dea was replaced by Paddy Kisnorbo on Sunday against Cardiff, while Andy O'Brien, Leigh Bromby, and Alex Bruce are all available to come into contention."Losing Darren is disappointing because he's done really well over these past few weeks and formed a good partnership with Tom Lees," said the boss."Paddy came in and did very well on Sunday and Andy O'Brien has shown a real positive attitude and has done well over the past few weeks. He's looking strong and sharp."