Asked on www.om.net if he would be departing the French club, the 54-year-old replied: "Yes. It has been a while since I took that decision."
Gerets said he would be leaving the club because of the lack of trust between him and owner Robert Louis-Dreyfus, who told French daily L'Equipe in January he would wait until the end of the season to offer the coach a new contract.
"I got muddled after Robert Louis-Dreyfus's interview," Gerets told local newspaper La Provence.
"I did not understand and I still don't. I think it was a sign. Despite my work, there was a lack of gratitude and most of all a lack of trust.
"If I had been offered a new two-year contract with the same wage or a little bit more before the end of March, I would have signed immediately."
Marseille top the Ligue 1 table with five games of their season remaining, five points ahead of Girondins Bordeaux who have a game in hand.
The club were last crowned French champions in 1992 and the last major trophy they won was the 1993 Champions League.
A Louis-Dreyfus spokesman said the Marseille owner now wanted Gerets to stay but the coach had rejected the proposal.
"(Louis-Dreyfus) would have sent a strong message if he had told me as soon as January he wanted me to stay, while we were fourth in the league," Gerets told La Provence.
Gerets replaced Albert Emon in September 2007 after the club made a poor start to the season.
