Smith said: "We like Ayala and had a look at him but unfortunately he's cup-tied after playing in the UEFA Cup.
"We want players who are available for our Champions League campaign. We're looking to strengthen the midfield as Frank Lampard and Claude Makelele are looking a bit tired.
"If Petit and Veron were fit there wouldn't be a problem and we need to know when they'll be back."
Meanwhile, Claudio Ranieri has challenged his Chelsea players to show a defiant reaction to their weekend defeat by Bolton when they take on Aston Villa in the Carling Cup tonight.
Ranieri will be without several first-team players at Villa Park, with Adrian Mutu having joined Veron, Petit and Eidur Gudjohnsen on the sidelines.
Carlo Cudicini could also be rested, while Ranieri may decide not to risk full-back Glen Johnson, who sustained a slight ankle injury during the 2-1 defeat by Bolton last Saturday.
However, the Chelsea coach will still field a strong line-up, with the likes of Jimmy Floyd Hasselbaink, Mario Melchiot, William Gallas and Joe Cole looking to return to the side.
Ranieri admitted his team were "tired" during the second-half against Bolton, but insisted: "It's another day and now I want to see our reaction after the bad defeat we had against Bolton.
"It's an important competition for us and also for Aston Villa. David O'Leary said at the start of the season that he could not win the league, so everything was about the two cups. We know that and we are ready to fight."
Aston Villa v Chelsea, Villa Park, tonight, 7.45pm, (Live on SkySports 2)