The O's boss attempted to hand in his notice after his employers rejected an approach for his services from Championship outfit Cardiff City.
The club issued a statement on Wednesday confirming that Slade has offered his resignation, and they are now considering their response.
"The chairman and the CEO of Leyton Orient have received a resignation letter from Russell Slade a few minutes ago," said the Orient hierarchy.
"This has not happened by chance after the club rejected this afternoon, a proposal from the general manager of Cardiff City regarding the transfer of Russell Slade. The lawyers of the club are now studying the file."
Orient currently sit in 17th place in League One.