Nasri said on Monday that he had joined the Gunners, but those claims were swiftly rubbished by his agent and both clubs.
However, Diouf told Marseille's official website that a deal, while not yet complete, was imminent.
Diouf said: "We know Samir Nasri's position. Under the Webster ruling, he had the possibility of leaving the club for much less than the agreement we've reached today.
"After talks with him and his representatives, we've reached an agreement on the circumstances of his departure. Samir was approached in very concrete terms by Arsenal, who also contacted us.
"There are therefore steps that need to be taken to reach an agreement between the clubs.
"There is a strong chance he could play for (Arsenal) next season, but until the agreement is formalised we can't talk about any departure."