O'Neill - who has has fielded the same XI for all six Premier League games so far - believes the second-leg clash against the Bulgarians will give the likes of Milner and Cuellar the ideal chance to cement their place in the side for the trip to west London.
He said: "I don't think there is any point in them playing if they don't feel they've got a chance of breaking in.
"I didn't actually realise until someone mentioned it that we had gone in with the same starting line-up for all of the league games. I certainly wouldn't have envisaged that.
"Players will come in and out of the side and they may well come in and out even if we are winning games.
"James Milner, Carlos Cuellar, whoever, if they play well could put themselves in the frame for Chelsea. Cuellar is going to be some player. He has been very impressive and wants to play. Milner is desperate to play."




