United manager Sir Alex Ferguson has monitored Benzema's progress since the 21-year-old scored in a 1-1 Champions League second-round tie at Stade de Gerland in February 2008, and the France international has been earmarked as a possible replacement for Carlos Tevez should he leave.
Benzema has consistently maintained that he is keen to stay at Lyon and, although Aulas has insisted that he has no desire to part with the player, the chairman has admitted that a substantial bid could force him to sell.
Aulas said Benzema "said he wants to stay and I don't want to sell, so he is here at 99 per cent. However, Kaka should have not left Milan and he will join Real Madrid.
"We have entered spiral madness and I won't say that Karim is untransferable."
Benzema has previously expressed a preference to move to Spain rather than England should he leave Lyon, but he insists that he is not ready to push for a move this summer.
He said: "If there is a huge offer and the chairman tells me I have to go, I would probably leave. But I will not go and see him to ask to leave." Real Madrid have previously courted Benzema, but in a week when he has admitted an interest in signing Kaka and Cristiano Ronaldo, Real president Florentino Perez has now confirmed that he intends to sign Bayern Munich's French winger Franck Ribery.
Real sporting director Zinedine Zidane has urged Perez to target Ribery ahead of Ronaldo, but Perez admits that the club have still to discuss a deal with Bayern.
He said: "It would be a huge satisfaction to have Ribery with us as soon as next season, but we first have to talk to his club."
Meanwhile, Manchester City could face competition from Inter Milan for Barcelona forward Samuel Eto'o following the suggestion that Eto'o could move to the San Siro in a swap deal involving Inter's Zlatan Ibrahimovic.
Despite winning Serie A with Inter last season, the Swedish striker claims he is keen for a fresh challenge.