The transgression means that the Portuguese will be suspended for the next three domestic games, including his side's Carling Cup final against Villa later this month.
Related ArticlesAston Villa 1 Man Utd 1Liverpool and Man United should combine to fight common enemyUnited out for revenge against VillaUnited steward sacked in row over bannerRio Ferdinand art defenderSport on televisionOf equal concern for Ferguson will be the fact that Giggs was forced to leave the ground with his right arm in a sling. The winger landed heavily after a challenge with Steve Sidwell midway through the second half, and damaged his forearm in the process. He will have to await the results of an X-Ray to discover the full extent of the damage.
'It is very painful but hopefully he is going to be alright,' Ferguson said.
The United manager had no complaints about Walton's decision to go to his pocket for Nani's studs-up tackle. The referee explained afterwards that 'in the current climate it was a rash challenge' and Ferguson and O'Neill both agreed that it warranted a red card.
'He's gone in double-footed,' Ferguson added. 'You can't do that. It was a naïve tackle and it left the referee with no option.'
As well as missing out on a trip to Wembley, Nani will be required to sit out of United's next two Premier League matches, a trip to Goodison Park and a home fixture with West Ham, which after this draw have assumed even greater importance as United strive to wrest the lead of the table from Chelsea. 'They are important games,' Ferguson conceded.
Despite only taking one point from the match, Ferguson was nevertheless encouraged by the performance of his side.
'We worked our socks off, we were the better team,' he said. 'You try to get a result, but credit to the players, they were absolutely brilliant. We were very consistent in terms of performance, and we can be very pleased with that.'
Martin O'Neill, meanwhile, has been left fretting over the fitness of Petrov, who was replaced by Sidwell in the 65th minute with ankle injury which was the direct result of Nani's tackle.
'He is pretty sore at this minute,' O'Neill said. 'He thought he was going to be OK at half time, but he stiffened up. It must be really sore if he was unable to continue. The doctor said it is soft tissue, whatever that means, but he doesn't think there is any serious damage.'