Athletic, currently struggling in the Premiership after a great start to the season, come to Hillsborough at the perfect time after The Owls regained their confidence with vital back-to-back wins.
Manchester City have not allowed Nicky Weaver to play in the cup clash so David Lucas will come back into the team and Marcus Tudgay will be allowed to play after signing a permanent contract until 2010 for a nominal fee.
John Hills is suspended so Chris Brunt should take his place in midfield but Deon Burton has already played in the competition for Rotherham United so he will be cup tied
On the game itself, midfielder O'Brien is happy to take his mind off the rigours of league football and happy to play with no pressure.
He told Footymad: "The Charlton game will be a welcome break for us and there will be not as much pressure on us as there would be in the league because we are still in the relegation fight but hopefully we can enjoy the game and get something out of it.
"I don’t know if it will affect the league or not, we just have to take one game at a time but it is a game that we will enjoy and we will just take it from there."
Wood meanwhile will come up against Darren Bent, a dark horse to go to the World Cup with England this summer but the 20-year-old is relishing the prospect.
He said: "I don’t know how I will match up against Darren but we will see. But I am very much looking forward to it and it’s always good to play against England internationals so it will be great and hopefully we can get a good result.
"The FA Cup is a good distraction and something to look forward to. We have another week before the next league game so we can look at things in training and improve on things. But the Charlton game could come at a bad time because two back-to-back wins is important and we want to carry on in the league and keep winning."