Lyon had been keen to sell Gomis during the transfer window but he refused to be forced out and shunned moves to Newcastle United and Swansea City.
Aulas admits that Gomis now has an important part to play at the Stade Gerland and says it will be like having a new player in the squad.
"We have to consider him as a reinforcement and I am convinced he could be a key reinforcement," Aulas told L'Equipe.
"I am happy he is with us. The club needs him."
Gomis has so far failed to agree on a new contract at Lyon and reports suggest they would still be interested in selling him in January.